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  • 1.
    Ahuja, Rajeev
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    High-pressure structural transitions in Cm and Am0.5Cm0.5 binary alloy2006In: High Pressure Research, ISSN 0895-7959, E-ISSN 1477-2299, Vol. 26, no 4, p. 377-381Article in journal (Refereed)
    Abstract [en]

    The high-pressure behaviour of Cm and Am0.5Cm0.5 binary alloy is investigated theoretically using ab initio electronic structure methods. Our calculations reproduce the structural phase transitions, which are observed in recent experiment performed by Heathman et al. [S. Heathman, R.G. Haire, T. Le Bihan et al., Science 309 110 (2005)] and Lindbaum et al. [A. Lindbaum, S. Heathman, T. Le Bihan et al., J. Phys: Condens. Matter 15 S2297 (2003)]. Calculated transition pressures are in reasonable agreement with the experimental values. Calculations performed for an antiferromagnetic state are essential to reproduce the stability of Cm-III phase.

  • 2.
    Ahuja, Rajeev
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Sun, Z
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ab initio investigation on the phase stability of Ti3SiC2, Ti3Si0.5Ge0.5C2 and2006In: High Pressure Research, Vol. 26, p. 127-Article in journal (Refereed)
  • 3. Benson, Daryn
    et al.
    Li, Yanling
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Svensson, Gunnar
    Haussermann, Ulrich
    Lithium and Calcium Carbides with Polymeric Carbon Structures2013In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 52, no 11, p. 6402-6406Article in journal (Refereed)
    Abstract [en]

    We studied the binary carbide systems Li2C2 and CaC2 at high pressure using an evolutionary and ab initio random structure search methodology for crystal structure prediction. At ambient pressure Li2C2 and CaC2 represent salt-like acetylides consisting of C-2(2-) dumbbell anions. The systems develop into semimetals (P (3) over bar m1-Li2C2) and metals (Cmcm-Li2C2, Cmcm-CaC2, and Immm-CaC2) with polymeric anions (chains, layers, strands) at moderate pressures (below 20 GPa). Cmcm-CaC2 is energetically closely competing with the ground, state structure. Polyanionic forms of carbon 4 stabilized by electrostatic interactions with surrounding cations add a new feature to carbon chemistry. SemimetallicP (3) over bar m1-Li2C2 displays an electronic structure close to that of graphene. The pi* band, however, is hybridized with Li-sp states and changed into a bonding valence band. Metallic forms are predicted to be superconductors. Calculated critical temperatures may exceed 10 K for equilibrium volume structures.

  • 4.
    Bouibes, A.
    et al.
    Université de Lille 1 Sciences et Technologies, Polytech'Lille, LGCgE-Lille Nord de France.
    Zaoui, A.
    Université de Lille 1 Sciences et Technologies, Polytech'Lille, LGCgE-Lille Nord de France.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Promising optical characteristics of zinc peroxide from first-principles investigation2017In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 263, p. 6-9Article in journal (Refereed)
    Abstract [en]

    The structural, electronic and optical properties of zinc peroxide have been investigated using first principle pseudopotential method within generalized gradient approximation (GGA) proposed by Perdew-Burke-Ernzerhof (PBE) and also within Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional for the exchangecorrelation. An underestimated band gap (1.77 eV) along with the higher density of states and expanded energy bands around the Fermi level is obtained. The HSE06 approach corrects the band gap and allows a proper description of defects with energy levels close to the conduction band. According to the HSE06 calculations, the obtained band gap is 3.2 eV. This value is very close to semiconductors band gap such as TiO2 (3.1 eV). The dielectric constants are identified with respect to electronic band structure and are utilized to derive the other optical properties such as retractive index, energy loss function, reflectivity and absorption. This mainly shows that zinc peroxide is a poor absorber of visible light.

  • 5. Ding, Yang
    et al.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Shu, Jinfu
    Chow, Paul
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Mao, Ho-kwang
    Structural phase transition of vanadium at 69 GPa2007In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 98, no 8, p. 085502-Article in journal (Refereed)
    Abstract [en]

    A phase transition was observed at 63-69 GPa and room temperature in vanadium with synchrotron x-ray diffraction. The transition is characterized as a rhombohedral lattice distortion of the body-centered-cubic vanadium without a discontinuity in the pressure-volume data, thus representing a novel type of transition that has never been observed in elements. Instead of driven by the conventional s-d electronic transition mechanism, the phase transition could be associated with the softening of C-44 trigonal elasticity tensor that originates from the combination of Fermi surface nesting, band Jahn-Teller distortion, and electronic topological transition.

  • 6. Dubrovinsky, L.
    et al.
    Dubrovinskaia, N.
    Crichton, W. A.
    Mikhaylushkin, Arkady S.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Simak, S. I.
    Abrikosov, I. A.
    de Almeida, J. Souza
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ahuja, Rajeev B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Johansson, B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Noblest of all metals is structurally unstable at high pressure2007In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 98, no 4, p. 045503-Article in journal (Refereed)
    Abstract [en]

    In a series of experiments in externally electrically heated diamond anvil cells we demonstrate that at pressures above similar to 240 GPa gold adopts a hexagonal-close-packed structure. Ab initio calculations predict that at pressures about 250 GPa different stacking sequences of close-packed atomic layers in gold become virtually degenerate in energy, strongly supporting the experimental observations.

  • 7.
    Dubrovinsky, L.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Dubrovinskaia, N.
    S. de Almeida, J.
    Luo, Wei
    Crichton, W. A.
    Johansson, Börje
    Ahuja, Rajeev
    Relativistic Effects Driven Structural Phase Transition in Gold at High PressureIn: NatureArticle in journal (Refereed)
  • 8. Heathman, S.
    et al.
    Haire, R. G.
    Le Bihan, T.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Li, S.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    The unique high-pressure behavior of curiurn probed further using alloys2007In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 444, p. 138-141Article in journal (Refereed)
    Abstract [en]

    The changing role of the 5f electrons across the actinide series has been of prime interest for many years. The remarkable behavior of americium's 5f electrons under pressure was determined experimentally a few years ago and it precipitated a strong interest in the heavy element community. Theoretical treatments of americium's behavior under pressure followed and continue today. Experimental and theoretical findings regarding curium's behavior under pressure have shown that the pressure behavior of curium was not a mirror image of that for americium. Rather, one of the five crystallographic phases observed with curium (versus four for americium) was a unique monoclinic structure whose existence is due to a spin stabilization effect by curium's 5f(7) electronic configuration and its half-filled 5f-shell. We review briefly the behavior of pure curium under pressure but focus on the pressure behaviors of three curium alloys with the intent of comparing them with pure curium. An important experimental finding confirmed by theoretical computations, is that dilution of curium with its near neighbors is sufficient to prevent the formation of the unique C2/c phase that appears in pure Cm metal under pressure. As this unique C2/c phase is very sensitive to having a 5f7 configuration to maximize the magnetic spin polarization, dilution of this state with adjacent actinide neighbors reduces its stability.

  • 9. Johansson, Borje
    et al.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Li, Sa
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Cerium; Crystal Structure and Position in The Periodic Table2014In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 4, p. 6398-Article in journal (Refereed)
    Abstract [en]

    The properties of the cerium metal have intrigued physicists and chemists for many decades. In particular a lot of attention has been directed towards its high pressure behavior, where an isostructural volume collapse (gamma phase -> alpha phase) has been observed. Two main models of the electronic aspect of this transformation have been proposed; one where the 4f electron undergoes a change from being localized into an itinerant metallic state, and one where the focus is on the interaction between the 4f electron and the conduction electrons, often referred to as the Kondo volume collapse model. However, over the years it has been repeatedly questioned whether the cerium collapse really is isostructural. Most recently, detailed experiments have been able to remove this worrisome uncertainty. Therefore the isostructural aspect of the a-c transition has now to be seriously addressed in the theoretical modeling, something which has been very much neglected. A study of this fundamental characteristic of the cerium volume collapse is made in present paper and we show that the localized reversible arrow delocalized 4f electron picture provides an adequate description of this unique behavior. This agreement makes it possible to suggest that an appropriate crossroad position for cerium in The Periodic Table.

  • 10.
    Kaewmaraya, Thanayut
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Yang, Xiao
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Panigrahi, Puspamitra
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    A new, layered monoclinic phase of Co3O4 at high pressure2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 30, p. 19957-19961Article in journal (Refereed)
    Abstract [en]

    We present the crystal structures and electronic properties of a Co3O4 spinel under high pressure. Co3O4 undergoes a first-order transition from a cubic (CB) Fd (3) over barm to a lower-symmetry monoclinic (MC) P2(1)/c phase at 35 GPa, occurring after the local high-spin to low-spin phase transition. The high-pressure phase exhibits the octahedral coordination of Co(II) and Co(III), whereas the CB phase contains the fourfold coordination of Co(II) and the sixfold coordination of Co(III). The CB-to-MC transition is attributed to the charge-transfer between the di-and trivalent cations via the enhanced 3d-3d interactions.

  • 11. Kotmool, Komsilp
    et al.
    Kaewmaraya, Thanayut
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Chakraborty, Sudip
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Anversa, Jonas
    Bovornratanaraks, Thiti
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Gou, Huiyang
    Piquini, Paulo Cesar
    Kang, Tae Won
    Mao, Ho-Kwang
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Revealing an unusual transparent phase of superhard iron tetraboride under high pressure2014In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 111, no 48, p. 17050-17053Article in journal (Refereed)
    Abstract [en]

    First principles-based electronic structure calculations of super-hard iron tetraboride (FeB4) under high pressure have been undertaken in this study. Starting with a "conventional" superconducting phase of this material under high pressure leads to an unexpected phase transition toward a semiconducting one. This transition occurred at 53.7 GPa, and this pressure acts as a demarcation between two distinct crystal symmetries, metallic orthorhombic and semiconducting tetragonal phases, with Pnnm and I4(1)/acd space groups, respectively. In this work, the electron-phonon coupling-derived superconducting T-c has been determined up to 60 GPa and along with optical band gap variation with increasing pressure up to 300 GPa. The dynamic stability has been confirmed by phonon dispersion calculations throughout this study.

  • 12. Kulkarni, Shrinivas R.
    et al.
    Vennila, R. Selva
    Phatak, Nishad A.
    Saxena, S. K.
    Zha, C. S.
    El-Raghy, T.
    Barsoum, M. W.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Study of Ti2SC under compression up to 47 GPa2008In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 448, no 1-2, p. L1-L4Article in journal (Refereed)
    Abstract [en]

    The pressure dependence of the lattice parameters of the ternary layered carbide, Ti2SC, was measured by using synchrotron radiation X-ray diffraction and a diamond anvil cell setup. The experiment was conducted at room temperature and no phase transformation was observed up to the maximum pressure of 47 GPa. The a and c lattice parameters at room condition are 3.216 (A) over circle and 11.22 (A) over circle, respectively. The bulk modulus, calculated using the Birch-Murnaghan equation of state, is 191 +/- 3 GPa, with a pressure derivative of 4.0 +/- 0.3 and that obtained by our ab initio calculations is 183 GPa, with a pressure derivative of 4.1. L Like the majority of the ternary layered carbides (MAX phases), compressibility along the c-axis was higher than that along the a-axis.

  • 13.
    Li, Yan-Ling
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Chen, Xiao-Jia
    Zeng, Zhi
    Lin, Hai-Qing
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Formation of Nanofoam carbon and re-emergence of Superconductivity in compressed CaC62013In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 3, p. 3331-Article in journal (Refereed)
    Abstract [en]

    Pressure can tune material's electronic properties and control its quantum state, making some systems present disconnected superconducting region as observed in iron chalcogenides and heavy fermion CeCu2Si2. For CaC6 superconductor (T-c of 11.5 K), applying pressure firstTc increases and then suppresses and the superconductivity of this compound is eventually disappeared at about 18 GPa. Here, we report a theoretical finding of the re-emergence of superconductivity in heavily compressed CaC6. The predicted phase III (space group Pmmn) with formation of carbon nanofoam is found to be stable at wide pressure range with a Tc up to 14.7 K at 78 GPa. Diamond-like carbon structure is adhered to the phase IV (Cmcm) for compressed CaC6 after 126 GPa, which has bad metallic behavior, indicating again departure from superconductivity. Re-emerged superconductivity in compressed CaC6 paves a new way to design new-type superconductor by inserting metal into nanoporous host lattice.

  • 14.
    Li, Yan-Ling
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Zeng, Zhi
    Lin, Hai-Qing
    Mao, Ho-Kwang
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pressure-induced superconductivity in CaC22013In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 110, no 23, p. 9289-9294Article in journal (Refereed)
    Abstract [en]

    Carbon can exist as isolated dumbbell, 1D chain, 2D plane, and 3D network in carbon solids or carbon-based compounds, which attributes to its rich chemical binding way, including sp-, sp2-, and sp3-hybridized bonds. sp2-hybridizing carbon always captures special attention due to its unique physical and chemical property. Here, using an evolutionary algorithm in conjunction with ab initio method, we found that, under compression, dumbbell carbon in CaC2 can be polymerized first into 1D chain and then into ribbon and further into 2D graphite sheet at higher pressure. The C2/m structure transforms into an orthorhombicCmcm phase at 0.5 GPa, followed by another orthorhombic Immm phase, which is stabilized in a wide pressure range of 15.2–105.8 GPa and then forced into MgB2-type phase with wide range stability up to at least 1 TPa. Strong electron–phonon coupling λ in compressed CaC2 is found, in particular for Immmphase, which has the highest λ value (0.562–0.564) among them, leading to its high superconducting critical temperature Tc (7.9∼9.8 K), which is comparable with the 11.5 K value of CaC6. Our results show that calcium not only can stabilize carbon sp2 hybridization at a larger range of pressure but also can contribute in superconducting behavior, which would further ignite experimental and theoretical interest in alkaline–earth metal carbides to uncover their peculiar physical properties under extreme conditions.

  • 15.
    Li, Yunguo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Li, Yan-Ling
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Single-layer MoS2 as an efficient photocatalyst2013In: Catalysis Science & Technology, ISSN 2044-4753, Vol. 3, no 9, p. 2214-2220Article in journal (Refereed)
    Abstract [en]

    The potential application of the single-layer MoS2 as a photocatalyst was revealed based on first-principles calculations. It is found that the pristine single-layer MoS2 is a good candidate for hydrogen production, and its catalysing ability can be tuned by the applied mechanical strain. Furthermore, the p-type doping could make the single layer a good photocatalyst for the overall water splitting.

  • 16.
    Liu, Zeliang
    et al.
    Yanshan Univ, Coll Civil Engn & Mech, Key Lab Mech Reliabil Heavy Equipments & Large St, Qinhuangdao 066004, Peoples R China.;Yanshan Univ, State Key Lab Metastable Mat Sci & Technol, Qinhuangdao 066004, Peoples R China..
    Li, Huijian
    Yanshan Univ, Coll Civil Engn & Mech, Key Lab Mech Reliabil Heavy Equipments & Large St, Qinhuangdao 066004, Peoples R China..
    Fan, Changzeng
    Yanshan Univ, State Key Lab Metastable Mat Sci & Technol, Qinhuangdao 066004, Peoples R China..
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Necessary and sufficient elastic stability conditions in 21 quasicrystal Laue classes2017In: European journal of mechanics. A, Solids, ISSN 0997-7538, E-ISSN 1873-7285, Vol. 65, p. 30-39Article in journal (Refereed)
    Abstract [en]

    Mechanical stability is essential for solids and its stability criterion may date back to 75 years ago. Recently, the closed form necessary and sufficient conditions for elastic stability in all crystal classes have been investigated. Quasicrystals (QCs) are solids with long-range order and crystallographically forbidden rotational symmetries but without translational symmetry, attracting intense attentions in the last 30 years. In this work, we have explored the elastic constants and the elastic stability in detail for 1D, 2D and 3D QCs. All independent elastic constants and the closed form of necessary and sufficient conditions for elastic stability in all QCs classes are obtained, as a concise and pedagogical reference to stability criteria in aperiodic materials. Meanwhile, symmetry positions and stereographic projections of each QCs class are given as well.

  • 17.
    Luo, Wei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ab initio prediction of high-pressure structural phase transition in BaH22007In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 446, p. 405-408Article in journal (Refereed)
    Abstract [en]

    We have performed ab initio electronic structure calculations to calculate the structural properties and high-pressure phase transition in Barium dihydride (BaH2). Our results show that BaH2 crystallizes the orthorhombic phase (CoSi2-type structure) with Pnma space group at ambient conditions. A phase transition to the hexagonal (Ni2In-type structure) with P6(3)/mmc space group is found at pressure around 4 GPa. At the phase transition, the coordination number of hydrogen increases from 9 to 11 and the average bond length of Ba-H increases. The results show a band gap of 2.9 eV for orthorhombic and 1.8 eV for hexagonal phase. In addition, it was also found that more energy is required to desorb hydrogen atom from high-pressure phase as compared to ambient phase.

  • 18.
    Luo, Wei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Magnetic Fe(n+1)AC(n) (n=1, 2, 3, and A = Al, Si, Ge) phases: from ab initio theory2008In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 20, no 6, p. 064217-Article in journal (Refereed)
    Abstract [en]

    We have investigated the structural stability and magnetism for a set of compounds Fe(n+1)AC(n) (n = 1, 2, 3, and A = Al, Si, Ge) using ab initio theory. From our calculation, we have shown that some Fe(n+1)AC(n) phases (n = 2) with the general MAX phase formula and a layered hexagonal structure that belongs to space group D-6h(4)-P6(3)/mmc can have a combination of properties of the MAX phase at the same time as having magnetism. The Fe3AlC2 phase shows the most stable ferromagnetic properties among these MAX phases and the magnetic moment is 0.73 mu(B)/Fe atom. In addition, the phase stability is predicted by comparing the total energy of the Fe2AlC and Fe2SiC phases with the total energy of the competing equilibrium phases at the corresponding composition.

  • 19.
    Luo, Wei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Structural phase transitions in brookite-type TiO2 under high pressure2005In: Solid State Communications, Vol. 133, p. 49-Article in journal (Refereed)
  • 20.
    Luo, Wei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    de Almeida, J. Souza
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Osorio-Guillen, J. M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Electronic structure of a thermoelectric material: CsBi4Te62008In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 69, no 9, p. 2274-2276Article in journal (Refereed)
    Abstract [en]

    We have calculated the electronic structure of CsBi4Te6 by means of first-principles self-consistent total-energy calculations within the local-density approximation using the full-potential linear-muffin-tin-orbital method. From our calculated electronic structure we have calculated the frequency dependent dielectric function. Our calculations shows that CsBi4Te6 a semiconductor with a band gap of 0.3 eV. The calculated dielectric function is very anisotropic. Our calculated density of state support the recent experiment of Chung et al. [Science 287 (2000) 10241 that CsBi4Te6 is a high performance thermoelectric material for low temperature applications. (C) 2008 Elsevier Ltd. All rights reserved.

  • 21.
    Luo, Wei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Fang, C. M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    NANOLAYERED MAX PHASES FROM ab initio CALCULATIONS2008In: International Journal of Modern Physics B, ISSN 0217-9792, Vol. 22, no 25-26, p. 4495-4499Article in journal (Refereed)
    Abstract [en]

    The advancement in new materials processing and fabrication techniques has made it possible to better control the atomistic level of structures in a way, which was not feasible only a decade ago. If one can couple this atomic control with a good understanding of the relationship between structure and properties, this will in the future lead to a significant contribution to the synthesizing of tailor-made materials. In this paper we have focused on, the structurally related nanolayered ternary compounds M(N+1)AX(N), (MAX) where N = 1, 2 or 3, M is an early transition metal, A is an A-group (mostly IIIA and IVA) element, and X is either C and/or N, which has attracted increasing interest owing to their unique properties. The general relations between the electronic structure and materials properties of MAX phases have been elaborated based on ab initio calculations

  • 22.
    Luo, Wei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Arapan, Sergiu
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Souvatzis, Petros
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Katsnelson, Mikhail I.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Dynamical stability of body center cubic iron at the Earth's core conditions2010In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 107, no 22, p. 9962-9964Article in journal (Refereed)
    Abstract [en]

    Here, using self-consistent ab initio lattice dynamical calculations that go beyond the quasiharmonic approximation, we show that the high-pressure high-temperature bcc-Fe phase is dynamically stable. In this treatment the temperature-dependent phonon spectra are derived by exciting all the lattice vibrations, in which the phonon-phonon interactions are considered. The high-pressure and high-temperature bcc-Fe phase shows standard bcc-type phonon dispersion curves except for the transverse branch, which is overdamped along the high symmetry direction Gamma-N, at temperatures below 4,500 K. When lowering the temperature down to a critical value T-C, the lattice instability of the bcc structure is reached. The pressure dependence of this critical temperature is studied at conditions relevant for the Earth's core.

  • 23. Mao, Wendy L.
    et al.
    Wang, Lin
    Ding, Yang
    Yang, Wenge
    Liu, Wenjun
    Kim, Duck Young
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Meng, Yue
    Sinogeikin, Stas
    Shu, Jinfu
    Mao, Ho-Kwang
    Distortions and stabilization of simple-cubic calcium at high pressure and low temperature2010In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 107, no 22, p. 9965-9968Article in journal (Refereed)
    Abstract [en]

    Ca-III, the first superconducting calcium phase under pressure, was identified as simple-cubic (sc) by previous X-ray diffraction (XRD) experiments. In contrast, all previous theoretical calculations showed that sc had a higher enthalpy than many proposed structures and had an imaginary (unstable) phonon branch. By using our newly developed submicrometer high-pressure single-crystal XRD, cryogenic high-pressure XRD, and theoretical calculations, we demonstrate that Ca-III is neither exactly sc nor any of the lower-enthalpy phases, but sustains the sc-like, primitive unit by a rhombohedral distortion at 300 K and a monoclinic distortion below 30 K. This surprising discovery reveals a scenario that the high-pressure structure of calcium does not go to the zero-temperature global enthalpy minimum but is dictated by high-temperature anharmonicity and low-temperature metastability fine-tuned with phonon stability at the local minimum.

  • 24.
    Mir, Showkat H.
    et al.
    Cent Univ Gujarat, Ctr Nano Sci, Gandhinagar 382030, India..
    Jha, Prakash C.
    Cent Univ Gujarat, Sch Chem Sci, Gandhinagar 382030, India..
    Islam, Muhammed Shafiqul
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Banarjee, Amitava
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Dabhi, Shweta D.
    Maharaja Krishnakumarsinhji Bhavnagar Univ, Dept Phys, Bhavnagar 364001, Gujarat, India..
    Jha, Prafulla K.
    Maharaja Sayajirao Univ Baroda, Dept Phys, Fac Sci, Vadodara 390002, India..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Static and Dynamical Properties of heavy actinide Monopnictides of Lutetium2016In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, article id 29309Article in journal (Refereed)
    Abstract [en]

    In this work, density functional theory within the framework of generalized gradient approximation has been used to investigate the structural, elastic, mechanical, and phonon properties of lutetium monopnictides in rock-salt crystal structure. The spin orbit coupling and Hubbard-U corrections are included to correctly predict the essential properties of these compounds. The elastic constants, Young's modulus E, Poisson's ratio v, shear modulus G, anisotropy factor A and Pugh's ratio are computed. We found that all lutetium monopnictides are anisotropic and show brittle character. From the wave velocities along [100], [110] and [111] directions, melting temperature of lutetium monopnictides are predicted. Dynamical stability of these monopnictides has been studied by density functional perturbation theory.

  • 25.
    Naqvi, S. Rabab
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hussain, T.
    Univ Queensland, Australian Inst Bioengn & Nanotechnol, Ctr Theoret & Computat Mol Sci, Brisbane, Qld 4072, Australia..
    Panigrahi, P.
    Hindustan Univ, Ctr Clean Energy & Nano Convergence CENCON, Madras, Tamil Nadu, India..
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol KTH, Dept Mat & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Manipulating energy storage characteristics of ultrathin boron carbide monolayer under varied scandium doping2017In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 7, no 14, p. 8598-8605Article in journal (Refereed)
    Abstract [en]

    We report, for the first time we believe, a detailed investigation on hydrogen storage efficiency of scandium (Sc) decorated boron carbide (BC3) sheets using spin-polarized density functional theory (DFT). We analyzed the energetics of Sc adsorption and explored the most favorable adsorption sites of Sc on BC3 sheets with 3.12%, 6.25%, and 12.5% coverage effects. Our investigations revealed that Sc strongly binds on pristine BC3 sheet, with a minimum binding energy of similar to 5 eV, which is robust enough to hinder Sc-Sc metal clustering. Sc, the lightest transition metal, adsorbs a large number of H-2 molecules per atom, resulting in a reasonable storage capacity. With 12.5% Sc-coverage, functionalized BC3 sheets could attain a H2 storage capacity of 5.5 wt% with binding energies suitable for a practical H-2 storage medium.

  • 26.
    Naqvi, Syeda Rabab
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hussain, T.
    Univ Queensland, Australian Inst Bioengn & Nanotechnol, Ctr Theoret & Computat Mol Sci, Brisbane, Qld 4072, Australia..
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Exploring Doping Characteristics of Various Adatoms on Single-Layer Stanene2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 14, p. 7667-7676Article in journal (Refereed)
    Abstract [en]

    We have performed first-principles calculations based on density functional theory to investigate the doping characteristics of 31 different adatoms on stanene monolayer, which includes the elements of alkali metals (AM), alkaline earth metals (AEM), transition metals (TMs), and groups III-VII. The most stable configurations of all the dopants have been explored by calculating and comparing binding energies of all the possible binding sites. To comment on the uniform distribution of adatoms on stanene, the adsorption energies (E-ads) of adatoms have been compared with their experimental cohesive energies (E-c,) in the bulk phase.A further comparison reveals that the binding energies of most of the studied adatoms on stanene are much stronger than other group IV monolayers. Apart from structural and binding characteristics, bond lengths, adatom adatom distance, charge-transfer mechanism, electronic properties, and work function have also been explored in pristine and doped monolayers. The strong adsorption of adatoms on stanene, tunable electronic properties, and formation of dumbbell structures in the case of AEM and TM shows that doped stanene sheets are worth further exploration.

  • 27.
    Naqvi, Syeda Rabab
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rao, Gollu Sankar
    Univ Basel, Dept Phys, CH-4056 Basel, Switzerland..
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol KTH, Dept Mat & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Hussain, Tanveer
    Univ Queensland, Australian Inst Bioengn & Nanotechnol, Ctr Theoret & Computat Mol Sci, Brisbane, Qld 4072, Australia..
    Hexagonal Boron Nitride (h-BN) Sheets Decorated with OLi, ONa, and Li2F Molecules for Enhanced Energy Storage2017In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 18, no 5, p. 513-518Article in journal (Refereed)
    Abstract [en]

    First-principles electronic structure calculations were carried out on hexagonal boron nitride (h-BN) sheets functionalized with small molecules, such as OLi, ONa, and Li2F, to study their hydrogen (H-2) storage properties. We found that OLi and ONa strongly adsorb on h-BN sheets with reasonably large inter-adsorbent separations, which is desirable for H-2 storage. Ab initio molecular dynamics (MD) simulations further confirmed the structural stability of OLi-BN and ONa-BN systems at 400K. On the other hand, Li2F molecules form clusters over the surface of h-BN at higher temperatures. We performed a Bader charge investigation to explore the nature of binding between the functionalized molecules and h-BN sheets. The density of states (DOS) revealed that functionalized h-BN sheets become metallic with two-sided coverage of each type of molecules. Hydrogenation of OLi-BN and ONa-BN revealed that the functionalized systems adsorb multiple H-2 molecules around the Li and Na atoms, with H-2 adsorption energies ranging from 0.20 to 0.28eV, which is desirable for an efficient H-2 storage material.

  • 28.
    Parlak, Onur
    et al.
    Stanford Univ, Dept Mat Sci & Engn, Stanford, CA 94305 USA.;Linkoping Univ, IFM, Biosensors & Bioelect Ctr, S-58183 Linkoping, Sweden..
    Mishra, Yogendra Kumar
    Univ Kiel, Funct Nanomat, Inst Mat Sci, Kaiserstr 2, D-24143 Kiel, Germany..
    Grigoriev, Anton
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Mecklenburg, Matthias
    Hamburg Univ Technol, Inst Polymers & Composites, Denickestr 15, D-21073 Hamburg, Germany..
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Keene, Scott
    Stanford Univ, Dept Mat Sci & Engn, Stanford, CA 94305 USA..
    Salleo, Alberto
    Stanford Univ, Dept Mat Sci & Engn, Stanford, CA 94305 USA..
    Schulte, Karl
    Hamburg Univ Technol, Inst Polymers & Composites, Denickestr 15, D-21073 Hamburg, Germany..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Adelung, Rainer
    Univ Kiel, Funct Nanomat, Inst Mat Sci, Kaiserstr 2, D-24143 Kiel, Germany..
    Turner, Anthony P. F.
    Linkoping Univ, IFM, Biosensors & Bioelect Ctr, S-58183 Linkoping, Sweden..
    Tiwari, Ashutosh
    Linkoping Univ, IFM, Biosensors & Bioelect Ctr, S-58183 Linkoping, Sweden.;UCS, Inst Adv Mat, IAAM, Mjardevi Sci Pk,Teknikringen 4A, S-58330 Linkoping, Sweden..
    Hierarchical Aerographite nano-microtubular tetrapodal networks based electrodes as lightweight supercapacitor2017In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 34, p. 570-577Article in journal (Refereed)
    Abstract [en]

    A great deal of interest has been paid to the application of carbon-based nano-and microstructured materials as electrodes due to their relatively low-cost production, abundance, large surface area, high chemical stability, wide operating temperature range, and ease of processing including many more excellent features. The nanostructured carbon materials usually offer various micro-textures due to their varying degrees of graphitisation, a rich variety in terms of dimensionality as well as morphologies, extremely large surface accessibility and high electrical conductivity, etc. The possibilities of activating them by chemical and physical methods allow these materials to be produced with further higher surface area and controlled distribution of pores from nanoscale upto macroscopic dimensions, which actually play the most crucial role towards construction of the efficient electrode/electrolyte interfaces for capacitive processes in energy storage applications. Development of new carbon materials with extremely high surface areas could exhibit significant potential in this context and motivated by this in present work, we report for the first time the utilization of ultralight and extremely porous nano-microtubular Aerographite tetrapodal network as a functional interface to probe the electrochemical properties for capacitive energy storage. A simple and robust electrode fabrication strategy based on surface functionalized Aerographite with optimum porosity leads to significantly high specific capacitance (640 F/g) with high energy (14.2 Wh/kg) and power densities (9.67x103 W/kg) which has been discussed in detail.

  • 29. Phatak, Nishad A.
    et al.
    Kulkarni, Shrinivas R.
    Drozd, Vadym
    Saxena, Surendra K.
    Deng, Liwei
    Fei, Yingwei
    Hu, Jingzhu
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Synthesis and compressive behavior of Cr2GeC up to 48 GPa2008In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 463, no 1-2, p. 220-225Article in journal (Refereed)
    Abstract [en]

    M(n+1)AX(n) compounds have gathered huge momentum because of its exciting properties. In this paper we report the synthesis of ternary layered ceramic Cr2GeC, a 211 M(n+1)AX(n) compound by hot-pressing. Scanning electron microscopy and X-ray diffraction have been employed to characterize the new synthesized phase. High-pressure compressibility of Cr2GeC were measured using diamond anvil cell and synchrotron C radiation at room temperature up to 48 GPa. No phase transformation was observed in the experimental pressure range. The bulk modulus of Cr2GeC calculated using the Birch-Murnaghan equation of state is 169 +/- 3 GPa, with K' = 3.05 +/- 0.15.

  • 30.
    Ramzan, Muhammad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    High pressure, mechanical, and optical properties of ZrW2O82011In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 109, no 3, p. 033510-Article in journal (Refereed)
    Abstract [en]

    In this paper, we present the high pressure studies of well known negative thermal expansion material ZrW2O8 on the basis of our density functional theory calculations. We reproduce the experimental alpha and gamma crystal structures of ZrW2O8. We calculate the transition pressure (from alpha to gamma) of this material to be approximate to 26 kbar. Our calculated positional and axial parameters are in an excellent agreement with the available experimental values for the both alpha and gamma phases of this material. Then we study the mechanical properties of this material. We calculate the elastic constants, bulk, shear and Young's moduli, Poisson's ratio, and Debye temperature of alpha-ZrW2O8. In our study, we find that the generalized gradient approximation method fails to obtain the correct values while the local density approximation (LDA) method successfully reproduces the experimental bulk modulus of ZrW2O8. Our calculated values of the shear and Young's moduli, Poisson's ratio, and Debye temperature of alpha-ZrW2O8 with LDA method are also in good agreement with the experimental results. Finally, we predict and analyze the optical properties of this material.

  • 31.
    Shi, H
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Electronic and elastic properties of CaF2 under high pressure from ab initio calculations2009In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 21, no 41, p. 415501-Article in journal (Refereed)
    Abstract [en]

    Calcium fluoride CaF2 has been studied by using density functional theory (DFT) with the generalized gradient approximation (GGA). Our results demonstrate that the sequence of the pressure-induced structural transition of CaF2 is the fluorite structure (Fm (3) over barm), the orthorhombic cotunnite-type structure (Pnma), and the hexagonal Ni2In-type structure (P6(3)/mmc). The two transitions occur at pressures of 8 GPa and 105 GPa, accompanied by volume collapses of 8.4% and 1.2%, respectively. The energy band gap increases with pressure in the (Fm (3) over barm) and the forepart of Pnma phases. However, on increasing the pressure beyond 60 GPa, the gap decreases, which is due to the fluorine p(z)-states shifting toward the Fermi energy. In addition, the elastic properties versus pressure are also discussed. Our calculated elastic constants for the cubic phase at ambient pressure are in agreement with the experimental values. The stress-strain coefficient calculations show that shear transformations in the Pnma phase are more difficult than in the cubic phase and the compressibility along the c(h) (or a(o)) direction for the orthorhombic phase is stronger than that in the hexagonal crystal.

  • 32.
    Shi, H.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    First-principles calculations of the electronic structure and pressure-induced magnetic transition in siderite FeCO32008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 15, p. 155119-Article in journal (Refereed)
    Abstract [en]

    Rhombohedral siderite FeCO3 has been studied by using density-functional theory with the generalized gradient approximation (GGA). In order to take into account the strong on-site Coulomb interaction U present in FeCO3, we also performed the GGA+U calculations. We observe a pressure-induced magnetic transition (high spin -> low spin) at pressures of 15 and 28 GPa, which are underestimated with respect to the experiment, for the GGA and GGA+U calculations, respectively. This phase transition was with a volume collapse of 10% around, also accompanied by increases in bulk modulus, Young's modulus and sound velocity. The electronic density of states and charge-density calculations revealed that the magnetic transition was due to the pressure-induced Fe 3d electron delocalization.

  • 33. Springell, R.
    et al.
    Detlefs, B.
    Lander, G. H.
    Ward, R. C. C.
    Cowley, R. A.
    Ling, N.
    Goetze, W.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Elemental engineering: Epitaxial uranium thin films2008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 19, p. 193403-Article in journal (Refereed)
    Abstract [en]

    Epitaxial films of the well-known alpha (orthorhombic) structure and an unusual hcp form of uranium have been grown on Nb and Gd buffers, respectively, by sputtering techniques. In a 5000 A film of alpha-U a charge-density wave has been observed, and its properties are different from those found in the bulk. The 500 A hcp-U film has a c/a ratio of 1.90(1), which is unusually large for the hcp structure. Theoretical calculations show that this hcp form is metastable and predict that it orders magnetically.

  • 34. Srepusharawoot, P.
    et al.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bovornratanaraks, T.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pinsook, U.
    Evidence of a medium-range ordered phase and mechanical instabilities in strontium under high pressure2012In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 152, no 13, p. 1172-1175Article in journal (Refereed)
    Abstract [en]

    We provided the first theoretical evidence for a medium-range ordered phase in high pressure strontium from the first-principles calculations. At the absolute zero temperature, the enthalpy-pressure relation shows that the bcc and hcp are energetically more favorable than the other experimentally observed phases between 24 and 27 GPa. In the present work, we concentrate on the bcc phase because we found a link to a medium-range ordered phase. Our results reveal that the bcc phonon dispersion at the N and H points starts softening at around 24.1 GPa. The ab initio molecular dynamics at 300 K and 27 GPa showed that the bcc is quickly transformed into a lower energy structure with R3c symmetry and distorted basis. The simulated diffraction patterns showed that the R3c structure has only a single major peak at low angle. The R3c peak locates near the first peak of the bcc structure. This is the evidence of the so-called medium-range ordered phase. This structure is a strong candidate for the unsolved S-phase reported by experiments.

  • 35.
    Sun, Weiwei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Role of correlation and relativistic effects in MAX phases2012In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 47, no 21, p. 7615-7620Article in journal (Refereed)
    Abstract [en]

    We have performed the ab initio calculations to study the role of correlation and relativistic effects in MAX phases. As of now, there are more than 50 MAX phases reported in the literature; however, we have chosen two MAX phases, namely Cr2AlC and Ta2AlC, as representatives of MAX phases for our study as they are very poorly described from calculation point of view. Our results show that correlation effects are very important to understand the electronic and mechanical properties of Cr2AlC, but not so important for Ta2AlC. We have also studied the relativistic effects on Ta2AlC and our calculations show that going from scalar to fully relativistic effects does not have any significant effect on the electronic and mechanical properties of Ta2AlC. We conclude that Ta2AlC is a weakly correlated system, whereas Cr2AlC is a strongly correlated system. Further experiments are needed to explain the discrepancy between theory and experiments.

  • 36.
    Sun, Weiwei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Dept Mat Sci & Engn, SE-10044 Stockholm, Sweden..
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Dept Mat Sci & Engn, SE-10044 Stockholm, Sweden..
    Stability of a new cubic monoxide of Thorium under pressure2015In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, article id 13740Article in journal (Refereed)
    Abstract [en]

    Density functional theory has been applied to elucidate the stability of thorium monoxide (ThO). It is found out that the pressure can stabilize the rocksalt phase of ThO, and the transition pressure is estimated between 14 and 22 GPa. The stability of ThO can be attributed due to the gradually filling 5f orbitals at the expense of 7s and 6d electrons in Th metal. For ThO, the pressure induces stronger Th-O bond reflected by the newly established 6d-2p hybridization which is the dominant cause of its stability. The phonon dispersion curves of the rocksalt phase show the positive frequencies which indicates its dynamical stability. Our successful prediction of the stabilization of the metallic ThO has proposed a route to synthesize novel actinide monoxides.

  • 37.
    Sun, Weiwei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Dept Mat Sci & Engn, SE-10044 Stockholm, Sweden..
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Feng, Qingguo
    Linkoping Univ, Dept Phys Chem & Biol, SE-58183 Linkoping, Sweden.;Linkoping Univ, SeRC, SE-58183 Linkoping, Sweden..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Dept Mat Sci & Engn, SE-10044 Stockholm, Sweden..
    Anisotropic distortion and Lifshitz transition in alpha-Hf under pressure2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 11, article id 115130Article in journal (Refereed)
    Abstract [en]

    In this work we report a theoretical investigation on behavior of the elastic constant C-44 and the transverse optical phonon mode E(2)g of a-Hf under pressure within the density functional theory. In contrast to many other reported transition metals, the above two quantities do not show a synchronous relation as pressure increases. Below 13 GPa, an opposite shifting tendency has been observed. However, once the pressure is raised above 13 GPa, the trend is pulled back to be consistent. This anomalous behavior is figured out to be caused by the large lattice anisotropy of the c/a ratio along with the elastic anisotropy. The synchronous behavior is found to be in accordance with the behavior of c/a ratio with increased pressure. In our band-structure investigations the electronic topological transition has been discovered at 10 GPa, which relates to the change of c/a ratio suggested by recent literature. The presence of the Van Hove singularity shown in the densities of states has been identified and regarded as the origin of the variation of C-44 and E(2)g.

  • 38.
    Tsuppayakorn-aek, Prutthipong
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Chulalongkorn Univ, ECPRL, Dept Phys, Fac Sci, Bangkok 10330, Thailand.;Chulalongkorn Univ, PEMRU, Dept Phys, Fac Sci, Bangkok 10330, Thailand.;Commiss Higher Educ, Thailand Ctr Excellence Phys, 328 Si Ayutthaya Rd, Bangkok 10400, Thailand..
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol KTH, Appl Mat Phys, Dept Mat & Engn, SE-10044 Stockholm, Sweden..
    Bovornratanaraks, Thiti
    Chulalongkorn Univ, ECPRL, Dept Phys, Fac Sci, Bangkok 10330, Thailand.;Chulalongkorn Univ, PEMRU, Dept Phys, Fac Sci, Bangkok 10330, Thailand.;Commiss Higher Educ, Thailand Ctr Excellence Phys, 328 Si Ayutthaya Rd, Bangkok 10400, Thailand..
    The High-Pressure Superconducting Phase of Arsenic2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 3026Article in journal (Refereed)
    Abstract [en]

    Ab initio random structure searching (AIRSS) technique is predicted a stable structure of arsenic (As). We find that the body-centered tetragonal (bct) structure with spacegroup I4(1)/acd to be the stable structure at high pressure. Our calculation suggests transition sequence from the simple cubic (sc) structure transforms into the host-guest (HG) structure at 41 GPa and then into the bct structure at 81 GPa. The bct structure has been calculated using ab initio lattice dynamics with finite displacement method confirm the stability at high pressure. The spectral function alpha F-2 of the bct structure is higher than those of the body-centered cubic (bcc) structure. It is worth noting that both bct and bcc structures share the remarkable similarity of structural and property. Here we have reported the prediction of temperature superconductivity of the bct structure, with a T-c of 4.2 K at 150 GPa.

  • 39.
    Tsuppayakorn-aek, Prutthipong
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Chulalongkorn Univ, Fac Sci, ECPRL, Bangkok 10330, Thailand;Chulalongkorn Univ, Fac Sci, PEMRU, Dept Phys, Bangkok 10330, Thailand;Thailand Ctr Excellence Phys, Commiss Higher Educ, 328 Si Ayutthaya Rd, Bangkok 10400, Thailand.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Watcharatharapong, Teeraphat
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol KTH, Dept Mat & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden.
    Bovornratanaraks, Thiti
    Chulalongkorn Univ, Fac Sci, ECPRL, Bangkok 10330, Thailand;Chulalongkorn Univ, Fac Sci, PEMRU, Dept Phys, Bangkok 10330, Thailand;Thailand Ctr Excellence Phys, Commiss Higher Educ, 328 Si Ayutthaya Rd, Bangkok 10400, Thailand.
    Structural prediction of host-guest structure in lithium at high pressure2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 5278Article in journal (Refereed)
    Abstract [en]

    Ab initio random structure searching (AIRSS) technique is used to identify the high-pressure phases of lithium (Li). We proposed the transition mechanism from the fcc to host-guest (HG) structures at finite temperature and high pressure. This complex structural phase transformation has been calculated using ab initio lattice dynamics with finite displacement method which confirms the dynamical harmonic stabilization of the HG structure. The electron distribution between the host-host atoms has also been investigated by electron localization function (ELF). The strongly localized electron of p bond has led to the stability of the HG structure. This remarkable result put the HG structure to be a common high-pressure structure among alkali metals.

  • 40.
    Yang, Xiao
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Yanshan Univ, Coll Civil Engn & Mech, Qin Huangdao 066004, Hebei, Peoples R China..
    Li, Huijian
    Yanshan Univ, Coll Civil Engn & Mech, Qin Huangdao 066004, Hebei, Peoples R China..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol KTH, Dept Mat & Engn, S-10044 Stockholm, Sweden..
    Kang, Taewon
    Dongguk Univ, Nano Informat Technol Acad, Seoul 100715, South Korea..
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Dongguk Univ, Nano Informat Technol Acad, Seoul 100715, South Korea..
    Formation and electronic properties of palladium hydrides and palladium-rhodium dihydride alloys under pressure2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 3520Article in journal (Refereed)
    Abstract [en]

    We present the formation possibility for Pd-hydrides and Pd-Rh hydrides system by density functional theory (DFT) in high pressure upto 50 GPa. Calculation confirmed that PdH2 in face-centered cubic (fcc) structure is not stable under compression that will decomposition to fcc-PdH and H-2. But it can be formed under high pressure while the palladium is involved in the reaction. We also indicate a probably reason why PdH2 can not be synthesised in experiment due to PdH is most favourite to be formed in Pd and H-2 environment from ambient to higher pressure. With Rh doped, the Pd-Rh dihydrides are stabilized in fcc structure for 25% and 75% doping and in tetragonal structure for 50% doping, and can be formed from Pd, Rh and H-2 at high pressure. The electronic structural study on fcc type PdxRh1-xH2 indicates the electronic and structural transition from metallic to semi-metallic as Pd increased from x = 0 to 1.

  • 41.
    Yang, Xiao
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Yanshan Univ, Coll Civil Engn & Mech, Qin Huangdao 066004, Hebei, Peoples R China.
    Li, Huijian
    Yanshan Univ, Coll Civil Engn & Mech, Qin Huangdao 066004, Hebei, Peoples R China..
    Hu, Minzheng
    Yanshan Univ, Coll Civil Engn & Mech, Qin Huangdao 066004, Hebei, Peoples R China..
    Liu, Zeliang
    Yanshan Univ, Coll Civil Engn & Mech, Qin Huangdao 066004, Hebei, Peoples R China..
    Wärnå, John
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Cao, Yuying
    Deakin Univ, Inst Frontier Mat, Geelong, Vic 3216, Australia..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Mechanical properties investigation on single-wall ZrO2 nanotubes: A finite element method with equivalent Poisson's ratio for chemical bonds2018In: Physica. E, Low-Dimensional systems and nanostructures, ISSN 1386-9477, E-ISSN 1873-1759, Vol. 98, p. 23-28Article in journal (Refereed)
    Abstract [en]

    A method to obtain the equivalent Poisson's ratio in chemical bonds as classical beams with finite element method was proposed from experimental data. The UFF (Universal Force Field) method was employed to calculate the elastic force constants of Zr-O bonds. By applying the equivalent Poisson's ratio, the mechanical properties of single-wall ZrNTs (ZrO2 nanotubes) were investigated by finite element analysis. The nanotubes' Young's modulus (Y), Poisson's ratio (nu) of ZrNTs as function of diameters, length and chirality have been discussed, respectively. We found that the Young's modulus of single-wall ZrNTs is calculated to be between 350 and 420 GPa.

  • 42. Zeng, Qiao-Shi
    et al.
    Ding, Yang
    Mao, Wendy L
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Blomqvist, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Yang, Wenge
    Shu, Jinfu
    Sinogeikin, Stas V
    Meng, Yue
    Brewe, Dale L
    Jiang, Jian-Zhong
    Mao, Ho-Kwang
    Substitutional alloy of Ce and Al2009In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 106, no 8, p. 2515-2518Article in journal (Refereed)
    Abstract [en]

    The formation of substitutional alloys has been restricted to elements with similar atomic radii and electronegativity. Using high-pressure at 298 K, we synthesized a face-centered cubic disordered alloy of highly dissimilar elements (large Ce and small Al atoms) by compressing the Ce(3)Al intermetallic compound >15 GPa or the Ce(3)Al metallic glass >25 GPa. Synchrotron X-ray diffraction, Ce L(3)-edge absorption spectroscopy, and ab initio calculations revealed that the pressure-induced Kondo volume collapse and 4f electron delocalization of Ce reduced the differences between Ce and Al and brought them within the Hume-Rothery (HR) limit for substitutional alloying. The alloy remained after complete release of pressure, which was also accompanied by the transformation of Ce back to its ambient 4f electron localized state and reversal of the Kondo volume collapse, resulting in a non-HR alloy at ambient conditions.

  • 43. Zhang, Xinyu
    et al.
    Qin, Jiaqian
    Liu, Hanyu
    Zhang, Shiliang
    Ma, Mingzhen
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Liu, Riping
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pressure-induced zigzag phosphorus chain and superconductivity in boron monophosphide2015In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, article id 8761Article in journal (Refereed)
    Abstract [en]

    We report on the prediction of the zinc-blende structure BP into a novel C2/m phase from 113 to 208 GPa which possesses zigzag phosphorus chain structure, followed by another P4(2)/mnm structure above 208 GPa above using the particle-swarm search method. Strong electron-phonon coupling lambda in compressed BP is found, in particular for C2/m phase with the zigzag phosphorus chain, which has the highest lambda (0.56-0.61) value among them, leading to its high superconducting critical temperature T-c (9.4 K-11.5 K), which is comparable with the 4.5 Kto 13 Kvalue of black phosphorus phase I (orthorhombic, Cmca). This is the first system in the boron phosphides which shows superconductivity from the present theoretical calculations. Our results show that pressure-induced zigzag phosphorus chain in BP exhibit higher superconducting temperature T-C, opening a new route to search and design new superconductor materials with zigzag phosphorus chains.

1 - 43 of 43
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