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BETA
Hermansson, Kersti, ProfessorORCID iD iconorcid.org/0000-0003-2352-0458
Alternative names
Publications (10 of 229) Show all publications
Kettner, M., Duchon, T., Wolf, M. J., Kullgren, J., Senanayake, S. D., Hermansson, K., . . . Nehasil, V. (2019). Anion-mediated electronic effects in reducible oxides: Tuning the valence band of ceria via fluorine doping. Journal of Chemical Physics, 151(4), Article ID 044701.
Open this publication in new window or tab >>Anion-mediated electronic effects in reducible oxides: Tuning the valence band of ceria via fluorine doping
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2019 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 151, no 4, article id 044701Article in journal (Refereed) Published
Abstract [en]

Combining experimental spectroscopy and hybrid density functional theory calculations, we show that the incorporation of fluoride ions into a prototypical reducible oxide surface, namely, ceria(111), can induce a variety of nontrivial changes to the local electronic structure, beyond the expected increase in the number of Ce3+ ions. Our resonant photoemission spectroscopy results reveal new states above, within, and below the valence band, which are unique to the presence of fluoride ions at the surface. With the help of hybrid density functional calculations, we show that the different states arise from fluoride ions in different atomic layers in the near surface region. In particular, we identify a structure in which a fluoride ion substitutes for an oxygen ion at the surface, with a second fluoride ion on top of a surface Ce4+ ion giving rise to F 2p states which overlap the top of the O 2p band. The nature of this adsorbate F--Ce4+ resonant enhancement feature suggests that this bond is at least partially covalent. Our results demonstrate the versatility of anion doping as a potential means of tuning the valence band electronic structure of ceria.

National Category
Theoretical Chemistry Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-393127 (URN)10.1063/1.5109955 (DOI)000478625700040 ()31370552 (PubMedID)
Funder
Swedish Research CouncileSSENCE - An eScience Collaboration
Note

M. Kettner, T. Duchoň, and M. J. Wolf contributed equally to this work.

Available from: 2019-09-24 Created: 2019-09-24 Last updated: 2019-09-24Bibliographically approved
Kebede, G., Mitev, P. D., Broqvist, P., Eriksson, A. & Hermansson, K. (2019). Fifty Shades of Water: Benchmarking DFT Functionals against Experimental Data for Ionic Crystalline Hydrates. Journal of Chemical Theory and Computation, 15(1), 584-594
Open this publication in new window or tab >>Fifty Shades of Water: Benchmarking DFT Functionals against Experimental Data for Ionic Crystalline Hydrates
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2019 (English)In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 15, no 1, p. 584-594Article in journal (Refereed) Published
Abstract [en]

We propose that crystalline ionic hydrates constitute a valuable resource for benchmarking theoretical methods for aqueous ionic systems. Many such structures are known from the experimental literature, and they contain a large variety of water–water and ion–water structural motifs. Here we have collected a data set (CRYSTALWATER50) of 50 structurally unique "in-crystal" water molecules, involved in close to 100 nonequivalent O–H···O hydrogen bonds. A dozen well-known DFT functionals were benchmarked with respect to their ability to describe these experimental structures and their OH vibrational frequencies. We find that the PBE, RPBE-D3, and optPBE-vdW methods give the best H-bond distances and that anharmonic OH frequencies generated from B3LYP//optPBE-vdW energy scans outperform the other methods, i.e., here we performed B3LYP energy scans along the OH stretching coordinate while the rest of the structure was kept fixed at the optPBE-vdW-optimized positions.

National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:uu:diva-347222 (URN)10.1021/acs.jctc.8b00423 (DOI)000455558200051 ()30380849 (PubMedID)
Funder
Swedish Research CouncileSSENCE - An eScience Collaboration
Note

Title in thesis list of papers: Fifty shades of water: Benchmarking DFT functionals against diffraction and spectroscopic data for crystalline hydrates

Available from: 2018-03-27 Created: 2018-03-27 Last updated: 2019-02-19Bibliographically approved
Du, D., Kullgren, J., Hermansson, K. & Broqvist, P. (2019). From Ceria Clusters to Nanoparticles: Superoxides and Supercharging. The Journal of Physical Chemistry C, 123(3), 1742-1750
Open this publication in new window or tab >>From Ceria Clusters to Nanoparticles: Superoxides and Supercharging
2019 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 3, p. 1742-1750Article in journal (Refereed) Published
Abstract [en]

Several studies have reported a dramatically increased oxygen storage capacity (OSC) for small ceria nanoparticles (∼5 nm). Both experiments and theory have correlated this effect with superoxide ion formation. In previous studies, density functional theory (DFT) calculations with the PBE+U density functional have been used, and the obtained results were only in qualitative agreement with the experimental observations. One severe problem is the underbinding of the O2 molecule upon superoxide ion formation, which suggests that such species should not exist above room temperature. In this work, we use hybrid DFT functional to resolve this problem. We find that the discrepancy between theory and experiment originates from an incorrect estimate of the energy associated with the localized f-electrons with respect to the oxygen p-levels. By using average O2 adsorption energies from hybrid DFT calculations, extrapolated to large nanoparticles (3−10 nm), in conjunction with first-order desorption kinetics, we find that superoxide ions are indeed stable on nanosized ceria well above room temperature, in accordance with experiments.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2019
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:uu:diva-377356 (URN)10.1021/acs.jpcc.8b08977 (DOI)000457067500025 ()
Funder
Swedish Research CouncilÅForsk (Ångpanneföreningen's Foundation for Research and Development)eSSENCE - An eScience Collaboration
Available from: 2019-02-19 Created: 2019-02-19 Last updated: 2019-04-24Bibliographically approved
Cheng, C., Zhang, X., Yang, Z. & Hermansson, K. (2019). Identification of High-Performance Single-Atom MXenes Catalysts for Low-Temperature CO Oxidation. ADVANCED THEORY AND SIMULATIONS, 2(8), Article ID 1900006.
Open this publication in new window or tab >>Identification of High-Performance Single-Atom MXenes Catalysts for Low-Temperature CO Oxidation
2019 (English)In: ADVANCED THEORY AND SIMULATIONS, ISSN 2513-0390, Vol. 2, no 8, article id 1900006Article in journal (Refereed) Published
Abstract [en]

On the basis of first-principles calculations, Fe, Co, Ni, Cu, Zn, Ru, Rh, Ag, Ir, Pt, and Au decorated Mo2CO2-delta monolayers are investigated as potential single-atom catalyst (SAC) candidates for low-temperature CO oxidation reaction. From a first screening based on intuitive criteria concerning metal sintering, CO poisoning, and O-2 adsorption strength, the Zn/Mo2CO2-delta system is selected for further scrutiny by means of reactivity calculations for different CO concentrations. A lower barrier is found for Eley-Rideal reaction mechanism than for the Langmuir-Hinshelwood mechanism. The low Eley-Rideal barrier (0.15 eV) is attributed to the fact that the Zn atom weakens the O-O bond considerably and the electrophilic attack of CO weakens it further. The main conclusion is that this system is a promising low-temperature SAC candidate with a lower energy barrier for CO oxidation than noble metal and other 2D SAC systems investigated.

Place, publisher, year, edition, pages
WILEY-V C H VERLAG GMBH, 2019
Keywords
density functional theory, low-temperature CO oxidation, Mo2CO2, MXene, screening, single-atom catalysts
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-393342 (URN)10.1002/adts.201900006 (DOI)000478744400001 ()
Funder
Swedish Research Council
Available from: 2019-09-27 Created: 2019-09-27 Last updated: 2019-09-27Bibliographically approved
Kim, B.-H., Kullgren, J., Wolf, M. J., Hermansson, K. & Broqvist, P. (2019). Multiscale Modeling of Agglomerated Ceria Nanoparticles: Interface Stability and Oxygen Vacancy Formation. Frontiers in Chemistry, 7, Article ID 203.
Open this publication in new window or tab >>Multiscale Modeling of Agglomerated Ceria Nanoparticles: Interface Stability and Oxygen Vacancy Formation
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2019 (English)In: Frontiers in Chemistry, E-ISSN 2296-2646, Vol. 7, article id 203Article in journal (Refereed) Published
Abstract [en]

The interface formation and its effect on redox processes in agglomerated ceria nanoparticles (NPs) have been investigated using a multiscale simulation approach with standard density functional theory (DFT), the self-consistent-charge density functional tight binding (SCC-DFTB) method, and a DFT-parameterized reactive force-field (ReaxFF). In particular, we have modeled Ce40O80 NP pairs, using SCC-DFTB and DFT, and longer chains and networks formed by Ce40O80 or Ce132O264 NPs, using ReaxFF molecular dynamics simulations. We find that the most stable {111}/{111} interface structure is coherent whereas the stable {100}/{100} structures can be either coherent or incoherent. The formation of {111}/{111} interfaces is found to have only a very small effect on the oxygen vacancy formation energy, E-vac. The opposite holds true for {100}/{100} interfaces, which exhibit significantly lower E-vac values than the bare surfaces, despite the fact that the interface formation eliminates reactive {100} facets. Our results pave the way for an increased understanding of ceria NP agglomeration.

Place, publisher, year, edition, pages
FRONTIERS MEDIA SA, 2019
Keywords
multiscale modeling, density functional theory, self-consistent charge density functional tight binding, reducible oxides, cerium dioxide, nanoparticles, agglomeration
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:uu:diva-385974 (URN)10.3389/fchem.2019.00203 (DOI)000468727800001 ()
Funder
Swedish Research CouncilÅForsk (Ångpanneföreningen's Foundation for Research and Development)eSSENCE - An eScience Collaboration
Available from: 2019-06-19 Created: 2019-06-19 Last updated: 2019-06-19Bibliographically approved
Sassolini, A., Colozza, N., Papa, E., Hermansson, K., Cacciotti, I. & Arduini, F. (2019). Screen-printed electrode as a cost-effective and miniaturized analytical tool for corrosion monitoring of re-inforced concrete. Electrochemistry communications, 98, 69-72
Open this publication in new window or tab >>Screen-printed electrode as a cost-effective and miniaturized analytical tool for corrosion monitoring of re-inforced concrete
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2019 (English)In: Electrochemistry communications, ISSN 1388-2481, E-ISSN 1873-1902, Vol. 98, p. 69-72Article in journal (Refereed) Published
Abstract [en]

Herein, we report the first electrochemical sensor based on a screen-printed electrode designed to evaluate the corrosion level in iron-reinforced concrete specimens. The combination of an Ag pseudoreference electrode with a gel polymeric electrolyte allows for fast, stable and cost-effective potentiometric measurements, suitable for evaluating the corrosion of iron bars embedded in concrete samples. The sensor was found to be capable of discriminating between a standard non-corroded sample and samples subject to corrosion due to the presence of chloride or carbonate in the concrete matrix. The potential in concrete-based specimens containing carbonate (pH 9, - 0.35 +/- 0.03 V) or chloride (4% w/w, - 0.52 +/- 0.01 V) was found to be more negative than in a standard concrete-based sample ( - 0.251 +/- 0.003 V), in agreement with the ASTM standard C876 method which uses a classical Cu/CuSO4 solid reference electrode. Our results demonstrate that a printed Ag pseudoreference electrode combined with KC1 agar provides an efficient and reliable electrochemical system for evaluating the corrosion of iron bars embedded in concrete-based structures.

National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-372642 (URN)10.1016/j.elecom.2018.11.023 (DOI)000454898600015 ()
Available from: 2019-01-08 Created: 2019-01-08 Last updated: 2019-01-28Bibliographically approved
Wolf, M. J., Castleton, C. W. M., Hermansson, K. & Kullgren, J. (2019). STM Images of Anionic Defects at CeO2(111)-A Theoretical Perspective. Frontiers in Chemistry, 7, Article ID 212.
Open this publication in new window or tab >>STM Images of Anionic Defects at CeO2(111)-A Theoretical Perspective
2019 (English)In: Frontiers in Chemistry, E-ISSN 2296-2646, Vol. 7, article id 212Article in journal (Refereed) Published
Abstract [en]

We present a theoretically oriented analysis of the appearance and properties of plausible candidates for the anionic defects observed in scanning tunneling microscopy (STM) experiments on CeO2(111). The simulations are based on density functional theory (DFT) and cover oxygen vacancies, fluorine impurities and hydroxyl groups in the surface and sub-surface layers. In the surface layer, all three appear as missing spots in the oxygen sublattice in filled state simulated STM images, but they are distinguishable in empty state images, where surface oxygen vacancies and hydroxyls appear as, respectively, diffuse and sharp bright features at oxygen sites, while fluorine defects appear as triangles of darkened Ce ions. In the sub-surface layer, all three defects present more complex patterns, with different combinations of brightened oxygen ion triangles and/or darkened Ce ion triangles, so we provide image maps to support experimental identification. We also discuss other properties that could be used to distinguish the defects, namely their diffusion rates and distributions.

Keywords
simulated STM images, cerium dioxide (CeO2), density functional theory, anionic defects, reducible oxide
National Category
Condensed Matter Physics Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-389601 (URN)10.3389/fchem.2019.00212 (DOI)000471137100001 ()
Funder
Swedish Research CouncileSSENCE - An eScience CollaborationÅForsk (Ångpanneföreningen's Foundation for Research and Development)
Available from: 2019-07-24 Created: 2019-07-24 Last updated: 2019-07-24Bibliographically approved
Barcaro, G., Sernenta, L., Monti, S., Carravetta, V., Broqvist, P., Kullgren, J. & Hermansson, K. (2018). Dynamical and Structural Characterization of the Adsorption of Fluorinated Alkane Chains onto CeO2. The Journal of Physical Chemistry C, 122(41), 23405-23413
Open this publication in new window or tab >>Dynamical and Structural Characterization of the Adsorption of Fluorinated Alkane Chains onto CeO2
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2018 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 41, p. 23405-23413Article in journal (Refereed) Published
Abstract [en]

The widespread use of ceria-based materials and the need to design suitable strategies to prepare eco-friendly CeO2 supports for effective catalytic screening induced us to extend our computational multiscale protocol to the modeling of the hybrid organic/oxide interface between prototypical fluorinated linear alkane chains (polyethylene-like oligomers) and low-index ceria surfaces. The combination of quantum chemistry calculations and classical reactive molecular dynamics simulations provides a comprehensive picture of the interface and discloses, at the atomic level, the main causes of typical adsorption modes. The data show that at room temperature. a moderate. percentage` of fluorine atoms (around 25%) can enhance the interaction of the organic chains by anchoring strongly pivotal fluorines to the channels of the underneath ceria (100) surface, whereas an excessive content can remarkably reduce this interaction because of the repulsion between fluorine and the negatively charged oxygen of the surface.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2018
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-369912 (URN)10.1021/acs.jpcc.8b05554 (DOI)000448087900019 ()
Available from: 2018-12-17 Created: 2018-12-17 Last updated: 2019-02-19Bibliographically approved
Kebede, G., Mitev, P. D., Broqvist, P., Kullgren, J. & Hermansson, K. (2018). Hydrogen-Bond Relations for Surface OH Species [Review]. The Journal of Physical Chemistry C, 122(9), 4849-4858
Open this publication in new window or tab >>Hydrogen-Bond Relations for Surface OH Species
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2018 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 9, p. 4849-4858Article, book review (Refereed) Published
Abstract [en]

This paper concerns thin water films and their hydrogen-bond patterns on ionic surfaces. As far as we are aware, this is the first time H-bond correlations for surface water and hydroxide species are presented in the literature while hydrogen-bond relations in the solid state have been scrutinized for at least five decades. Our data set, which was derived using density functional theory, consists of 116 unique surface OH groups–intact water molecules as well as hydroxides–on MgO(001), CaO(001) and NaCl(001), covering the whole range from strong to weak to no H-bonds. The intact surface water molecules are found to always be redshifted with respect to the gas-phase water OH vibrational frequency, whereas the surface hydroxide groups are either redshifted (OsH) or blueshifted (OHf) compared to the gas-phase OH frequency. The surface H-bond relations are compared with the traditional relations for bulk crystals. We find that the “ν(OH) vs R(H···O)” correlation curve for surface water does not coincide with the solid state curve: it is redshifted by about 200 cm–1 or more. The intact water molecules and hydroxide groups on the ionic surfaces essentially follow the same H-bond correlation curve.

Place, publisher, year, edition, pages
Uppsala: , 2018
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-347220 (URN)10.1021/acs.jpcc.7b10981 (DOI)000427331300013 ()
Funder
Swedish Research Council
Available from: 2018-03-27 Created: 2018-03-27 Last updated: 2019-02-19Bibliographically approved
Kim, B.-H., Park, M., Kim, G., Hermansson, K., Broqvist, P., Choi, H.-J. & Lee, K.-R. (2018). Indirect-to-Direct Band Gap Transition of Si Nanosheets: Effect of Biaxial Strain. The Journal of Physical Chemistry C, 122(27), 15297-15303
Open this publication in new window or tab >>Indirect-to-Direct Band Gap Transition of Si Nanosheets: Effect of Biaxial Strain
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2018 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 27, p. 15297-15303Article in journal (Refereed) Published
Abstract [en]

The effect of biaxial strain on the band structure of two-dimensional silicon nanosheets (Si NSs) with (111), (110), and (001) exposed surfaces was investigated by means of density functional theory calculations. For all the considered Si NSs, an indirect-to-direct band gap transition occurs as the lateral dimensions of Si NSs increase; that is, increasing lateral biaxial strain from compressive to tensile always enhances the direct band gap characteristics. Further analysis revealed the mechanism of the transition which is caused by preferential shifts of the conduction band edge at a specific k-point because of their bond characteristics. Our results explain a photoluminescence result of the (111) Si NSs [U. Kim et al., ACS Nano 2011,.5, 2176-2181] in terms of the plausible tensile strain imposed in the unoxidized inner layer by surface oxidation.

National Category
Materials Chemistry Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-362012 (URN)10.1021/acs.jpcc.8b02239 (DOI)000439003600028 ()
Funder
The Swedish Foundation for International Cooperation in Research and Higher Education (STINT), KO2016-6901
Available from: 2018-10-05 Created: 2018-10-05 Last updated: 2019-02-19Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-2352-0458

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