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Aquilante, Francesco
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Publications (10 of 24) Show all publications
Farahani, P., Roca-Sanjuán, D. & Aquilante, F. (2014). A Two-Scale Approach to Electron Correlation in Multiconfigurational Perturbation Theory. Journal of Computational Chemistry, 35(22), 1609-1617
Open this publication in new window or tab >>A Two-Scale Approach to Electron Correlation in Multiconfigurational Perturbation Theory
2014 (English)In: Journal of Computational Chemistry, ISSN 0192-8651, E-ISSN 1096-987X, Vol. 35, no 22, p. 1609-1617Article, review/survey (Refereed) Published
Abstract [en]

We present a new approach for the calculation of dynamicelectron correlation effects in large molecular systems usingmulticonfigurational second-order perturbation theory(CASPT2). The method is restricted to cases where partitioningof the molecular system into an active site and an environment is meaningful. Only dynamic correlation effects derivedfrom orbitals extending over the active site are included at theCASPT2 level of theory, whereas the correlation effects of theenvironment are retrieved at lower computational costs. Forsufficiently large systems, the small errors introduced by thisapproximation are contrasted by the substantial savings inboth storage and computational demands compared to thefull CASPT2 calculation. Provided that static correlation effectsare correctly taken into account for the whole system, the proposed scheme represent a hierarchical approach to the electron correlation problem, where two molecular scales aretreated each by means of the most suitable level of theory.

Place, publisher, year, edition, pages
John Wiley & Sons, 2014
Keywords
Multiconfigurational Perturbation theory, correlation energy, excited states, deoxythymidine, acrolein, coelentramide
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:uu:diva-228141 (URN)10.1002/jcc.23666 (DOI)000339958300001 ()
Available from: 2014-07-04 Created: 2014-07-04 Last updated: 2017-12-05Bibliographically approved
Delcey, M. G., Freitag, L., Pedersen, T. B., Aquilante, F., Lindh, R. & Gonzalez, L. (2014). Analytical gradients of complete active space self-consistent field energies using Cholesky decomposition: Geometry optimization and spin-state energetics of a ruthenium nitrosyl complex. Journal of Chemical Physics, 140(17), 174103
Open this publication in new window or tab >>Analytical gradients of complete active space self-consistent field energies using Cholesky decomposition: Geometry optimization and spin-state energetics of a ruthenium nitrosyl complex
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2014 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 140, no 17, p. 174103-Article in journal (Refereed) Published
Abstract [en]

We present a formulation of analytical energy gradients at the complete active space self-consistent field (CASSCF) level of theory employing density fitting (DF) techniques to enable efficient geometry optimizations of large systems. As an example, the ground and lowest triplet state geometries of a ruthenium nitrosyl complex are computed at the DF-CASSCF level of theory and compared with structures obtained from density functional theory (DFT) using the B3LYP, BP86, and M06L functionals. The average deviation of all bond lengths compared to the crystal structure is 0.042 angstrom at the DF-CASSCF level of theory, which is slightly larger but still comparable with the deviations obtained by the tested DFT functionals, e. g., 0.032 angstrom with M06L. Specifically, the root-mean-square deviation between the DF-CASSCF and best DFT coordinates, delivered by BP86, is only 0.08 angstrom for S-0 and 0.11 angstrom for T-1, indicating that the geometries are very similar. While keeping the mean energy gradient errors below 0.25%, the DF technique results in a 13-fold speedup compared to the conventional CASSCF geometry optimization algorithm. Additionally, we assess the singlet-triplet energy vertical and adiabatic differences with multiconfigurational second-order perturbation theory (CASPT2) using the DF-CASSCF and DFT optimized geometries. It is found that the vertical CASPT2 energies are relatively similar regardless of the geometry employed whereas the adiabatic singlet-triplet gaps are more sensitive to the chosen triplet geometry. (C) 2014 AIP Publishing LLC.

National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:uu:diva-227732 (URN)10.1063/1.4873349 (DOI)000336048000005 ()
Available from: 2014-06-30 Created: 2014-06-30 Last updated: 2017-12-05Bibliographically approved
Boström, J., Veryazov, V., Aquilante, F., Bondo Pedersen, T. & Lindh, R. (2014). Analytical gradients of the second-order Møller–Plesset energy using Cholesky decompositions. International Journal of Quantum Chemistry, 114(5), 321-327
Open this publication in new window or tab >>Analytical gradients of the second-order Møller–Plesset energy using Cholesky decompositions
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2014 (English)In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 114, no 5, p. 321-327Article in journal (Refereed) Published
Abstract [en]

An algorithm for computing analytical gradients of the second-order Møller–Plesset (MP2) energy using density fitting (DF) is presented. The algorithm assumes that the underlying canonical Hartree–Fock reference is obtained with the same auxiliary basis set, which we obtain by Cholesky decomposition (CD) of atomic electron repulsion integrals. CD is also used for the negative semidefinite MP2 amplitude matrix. Test calculations on the weakly interacting dimers of the S22 test set (Jurečka et al., Phys. Chem. Chem. Phys. 2006, 8, 1985) show that the geometry errors due to the auxiliary basis set are negligible. With double-zeta basis sets, the error due to the DF approximation in intermolecular bond lengths is better than 0.1 pm. The computational time is typically reduced by a factor of 6–7.

Keywords
Cholesky decomposition, density fitting, MP2, analytic gradients
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:uu:diva-210533 (URN)10.1002/qua.24563 (DOI)000329794400003 ()
Available from: 2013-11-08 Created: 2013-11-08 Last updated: 2017-12-06Bibliographically approved
Merlot, P., Kjaergaard, T., Helgaker, T., Lindh, R., Aquilante, F., Reine, S. & Pedersen, T. B. (2013). Attractive electron-electron interactions within robust local fitting approximations. Journal of Computational Chemistry, 34(17), 1486-1496
Open this publication in new window or tab >>Attractive electron-electron interactions within robust local fitting approximations
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2013 (English)In: Journal of Computational Chemistry, ISSN 0192-8651, E-ISSN 1096-987X, Vol. 34, no 17, p. 1486-1496Article in journal (Refereed) Published
Abstract [en]

An analysis of Dunlap's robust fitting approach reveals that the resulting two-electron integral matrix is not manifestly positive semidefinite when local fitting domains or non-Coulomb fitting metrics are used. We present a highly local approximate method for evaluating four-center two-electron integrals based on the resolution-of-the-identity (RI) approximation and apply it to the construction of the Coulomb and exchange contributions to the Fock matrix. In this pair-atomic resolution-of-the-identity (PARI) approach, atomic-orbital (AO) products are expanded in auxiliary functions centered on the two atoms associated with each product. Numerical tests indicate that in 1% or less of all HartreeFock and KohnSham calculations, the indefinite integral matrix causes nonconvergence in the self-consistent-field iterations. In these cases, the two-electron contribution to the total energy becomes negative, meaning that the electronic interaction is effectively attractive, and the total energy is dramatically lower than that obtained with exact integrals. In the vast majority of our test cases, however, the indefiniteness does not interfere with convergence. The total energy accuracy is comparable to that of the standard Coulomb-metric RI method. The speed-up compared with conventional algorithms is similar to the RI method for Coulomb contributions; exchange contributions are accelerated by a factor of up to eight with a triple-zeta quality basis set. A positive semidefinite integral matrix is recovered within PARI by introducing local auxiliary basis functions spanning the full AO product space, as may be achieved by using Cholesky-decomposition techniques. Local completion, however, slows down the algorithm to a level comparable with or below conventional calculations. 

Keywords
resolution-of-the-identity, density fitting, indefinite two-electron integral matrix, convergence problems, HartreeFock, density-functional theory
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-202890 (URN)10.1002/jcc.23284 (DOI)000319404800006 ()
Available from: 2013-07-01 Created: 2013-07-01 Last updated: 2017-12-06Bibliographically approved
Aquilante, F., Pedersen, T. B., Veryazov, V. & Lindh, R. (2013). MOLCAS—a software for multiconfigurational quantum chemistry calculations. Wiley Interdisciplinary Reviews: Computational Molecular Science, 3(2), 143-149
Open this publication in new window or tab >>MOLCAS—a software for multiconfigurational quantum chemistry calculations
2013 (English)In: Wiley Interdisciplinary Reviews: Computational Molecular Science, ISSN 1759-0876, Vol. 3, no 2, p. 143-149Article in journal (Refereed) Published
Abstract [en]

At variance, with most of the quantum chemistry software presently available, MOLCAS is a package that is specialized in multiconfigurational wave function theory (MC-WFT) rather than density functional theory (DFT). Given the much higher algorithmic complexity of MC-WFT versus DFT, an extraordinary effort needs to be made from the programming point of view to achieve state-of-the-art performance for large-scale calculations. In particular, a robust and efficient implementation of the Cholesky decomposition techniques for handling two-electron integrals has been developed which is unique to MOLCAS. Together with this 'Cholesky infrastructure', a powerful and multilayer graphical and scripting user interface is available, which is an essential ingredient for the setup of MC-WFT calculations. These two aspects of the MOLCAS software constitute the focus of the present report.

National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:uu:diva-181516 (URN)10.1002/wcms.1117 (DOI)000318044900003 ()
Available from: 2012-09-25 Created: 2012-09-25 Last updated: 2015-01-08Bibliographically approved
Manni, G. L., Ma, D., Aquiliante, F., Olsen, J. & Gagliardi, L. (2013). SplitGAS Method for Strong Correlation and the Challenging Case of Cr-2. Journal of Chemical Theory and Computation, 9(8), 3375-3384
Open this publication in new window or tab >>SplitGAS Method for Strong Correlation and the Challenging Case of Cr-2
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2013 (English)In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 9, no 8, p. 3375-3384Article in journal (Refereed) Published
Abstract [en]

A new multiconfigurational quantum chemical method, SplitGAS, is presented. The configuration interaction expansion, generated from a generalized active space, GAS, wave function is split in two parts, a principal part containing the most relevant configurations and an extended part containing less relevant, but not negligible, configurations. The partition is based on an orbital criterion. The SplitGAS method has been employed to study the HF, N-2, and Cr-2 molecules. The results on these systems, especially on the challenging, multiconfigurational Cr-2 molecule, are satisfactory. While SplitGAS is comparable with the GASSCF method in terms of memory requirements, it performs better than the complete active space method followed by second-order perturbation theory, CASPT2, in terms of equilibrium bond length, dissociation energy, and vibrational properties.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-207643 (URN)10.1021/ct400046n (DOI)000323193500012 ()
Available from: 2013-09-17 Created: 2013-09-17 Last updated: 2017-12-06Bibliographically approved
Daku, L. M., Aquilante, F., Robinson, T. W. & Hauser, A. (2012). Accurate Spin-State Energetics of Transition Metal Complexes. 1. CCSD(T), CASPT2, and DFT Study of [M(NCH)(6)](2+) (M = Fe, Co). Journal of Chemical Theory and Computation, 8(11), 4216-4231
Open this publication in new window or tab >>Accurate Spin-State Energetics of Transition Metal Complexes. 1. CCSD(T), CASPT2, and DFT Study of [M(NCH)(6)](2+) (M = Fe, Co)
2012 (English)In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 8, no 11, p. 4216-4231Article in journal (Refereed) Published
Abstract [en]

Highly accurate estimates of the high-spin/low-spin energy, difference Delta E-HL(el) in the high-spin complexes [Fe(NCH)(6)](2+) and [Co(NCH)(6)](2+) have been obtained from the results of CCSD(T) calculations extrapolated to the complete basis set limit. These estimates are shown to be strongly influenced by scalar relativistic effects. They have been used to assess the performances of the CASPT2 method and 30 density functionals of the GGA, meta-GGA, global hybrid, RSH, and double-hybrid types. For the CASPT2 method, the results of the assessment support the proposal [Kepenekian, M.; Robert, V.; Le Guennic, B. J. Chem. Phys. 2009, 131, 114702] that the ionization potential-electron affinity (IPEA) shift defining the zeroth-order Hamiltonian be raised from its standard value of 0.25 au to 0.50-0.70 au for the determination of Delta E-HL(el) in Fe(II) complexes with a [FeN6] core. At the DFT level, some of the assessed functionals proved to perform within chemical accuracy (+/- 350 cm(-1)) for the spin-state energetics of [Fe(NCH)(6)](2+), others for that of [Co(NCH)(6)](2+), but none of them simultaneously for both complexes. As demonstrated through a reparametrization of the CAM-PBEO range-separated hybrid, which led to a functional that performs within chemical accuracy for the spin-state energetics of both complexes, performing density functionals of broad applicability may be devised by including in their training sets highly accurate data like those reported here for [Fe(NCH)(6)](2+) and [Co(NCH)(6)](2+).

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-189163 (URN)10.1021/ct300592w (DOI)000311191900022 ()
Available from: 2012-12-25 Created: 2012-12-25 Last updated: 2017-12-06Bibliographically approved
Bostrom, J., Pitonak, M., Aquilante, F., Neogrady, P., Pedersen, T. B. & Lindh, R. (2012). Coupled Cluster and Moller-Plesset Perturbation Theory Calculations of Noncovalent Intermolecular Interactions using Density Fitting with Auxiliary Basis Sets from Cholesky Decompositions. Journal of Chemical Theory and Computation, 8(6), 1921-1928
Open this publication in new window or tab >>Coupled Cluster and Moller-Plesset Perturbation Theory Calculations of Noncovalent Intermolecular Interactions using Density Fitting with Auxiliary Basis Sets from Cholesky Decompositions
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2012 (English)In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 8, no 6, p. 1921-1928Article in journal (Refereed) Published
Abstract [en]

We compute noncovalent intermolecular interaction energies for the S22 test set [Phys. Chem. Chem. Phys. 2006, 8, 1985-1993] of molecules at the Moller-Plesset and coupled cluster levels of supermolecular theory using density fitting (DF) to approximate all two-electron integrals. The error due to the DF approximation is analyzed for a range of auxiliary basis sets derived from Cholesky decomposition (CD) in conjunction with correlation consistent and atomic natural orbital valence basis sets. A Cholesky decomposition threshold of 10(-4)E(h) for full molecular CD and its one-center approximation (1C-CD) generally yields errors below 0.03 kcal/mol, whereas 10(-3)E(h) is sufficient to obtain the same level of accuracy or better with the atomic CD (aCD) and atomic compact CD (acCD) auxiliary basis sets. Comparing to commonly used predefined auxiliary basis sets, we find that while the aCD and acCD sets are larger by a factor of 2-4 with triple-zeta AO basis sets, they provide results 1-2 orders of magnitude more accurate.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-178689 (URN)10.1021/ct3003018 (DOI)000305092400007 ()
Available from: 2012-08-02 Created: 2012-08-01 Last updated: 2017-12-07Bibliographically approved
Roca-Sanjuan, D., Aquilante, F. & Lindh, R. (2012). Multiconfiguration second-order perturbation theory approach to strong electron correlation in chemistry and photochemistry. Wiley Interdisciplinary Reviews: Computational Molecular Science, 2(4), 585-603
Open this publication in new window or tab >>Multiconfiguration second-order perturbation theory approach to strong electron correlation in chemistry and photochemistry
2012 (English)In: Wiley Interdisciplinary Reviews: Computational Molecular Science, ISSN 1759-0876, Vol. 2, no 4, p. 585-603Article, review/survey (Refereed) Published
Abstract [en]

Rooted in the very fundamental aspects of many chemical phenomena, and for the majority of photochemistry, is the onset of strongly interacting electronic configurations. To describe this challenging regime of strong electron correlation, an extraordinary effort has been put forward by a young generation of scientists in the development of theories 'beyond' standard wave function and density functional models. Despite their encouraging results, a twenty-and-more-year old approach still stands as the gold standard for these problems: multiconfiguration second-order perturbation theory based on complete active space reference wave function (CASSCF/CASPT2). We will present here a brief overview of the CASSCF/CASPT2 computational protocol, and of its role in our understanding of chemical and photochemical processes.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-178187 (URN)10.1002/wcms.97 (DOI)000305393700006 ()
Available from: 2012-07-31 Created: 2012-07-30 Last updated: 2015-01-08Bibliographically approved
La Macchia, G., Manni, G. L., Todorova, T. K., Brynda, M., Aquilante, F., Roos, B. O. & Gagliardi, L. (2010). On the Analysis of the Cr-Cr Multiple Bond in Several Classes of Dichromium Compounds. Inorganic Chemistry, 49(11), 5216-5222
Open this publication in new window or tab >>On the Analysis of the Cr-Cr Multiple Bond in Several Classes of Dichromium Compounds
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2010 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 49, no 11, p. 5216-5222Article in journal (Refereed) Published
Abstract [en]

Since the discovery of a formal quintuple bond in Ar’CrCrAr’ (CrCr = 1.835 angstrom) by Power and co-workers in 2005, many efforts have been dedicated to isolating dichromium species featuring quintuple-bond character. In the present study we investigate the electronic configuration of several, recently synthesized dichromium species with ligands using nitrogen to coordinate the metal centers. The bimetallic bond distances of Power’s compound and Cr-2-diazadiene (1) (CrCr = 1.803 angstrom) are compared to those found for Cr-2(mu-eta(2)-ArNC(R)NAr)(2) (2) (CrCr = 1.746 angstrom; R = H, Ar = 2,6-Et2C6H3), Cr-2(mu-eta(2)-(ArNC)-N-Xyl(H)NArXyl)(3) (3) (CrCr = 1.740(reduced)/1.817(neutral) angstrom; Ar-Xyl=2,6-C6H3-(CH3)(2)), Cr-2(mu-eta(2)-TippPyNMes)(2) (4) (CrCr = 1.749 angstrom; TippPyNMes = 6-(2,4,6-triisopropylphenyl)pyridin-2-yl (2,4,6-trimethylphenyl)-amide), and Cr-2(mu-eta(2)-DippNC(NMe2)N-Dipp)(2) (5) (CrCr = 1.729 angstrom, Dipp = 2,6-i-Pr2C6H3). We show that the correlation between the CrCr bond length and the effective bond order (EBO) is strongly affected by the nature of the ligand, as well as by the steric hindrance due to the ligand structure (e.g., the nature of the coordinating nitrogen). A linear correlation between the EBO and CrCr bond distance is established within the same group of ligands. As a result, the CrCr species based on the amidinate, aminopyridinate, and guanidinate ligands have bond patterns similar to the Ar’CrCrAr’ compound. Unlike these latter species, the dichromium diazadiene complex is characterized by a different bonding pattern involving Cr-N pi interactions, resulting in a lower bond order associated with the short metal-metal bond distance. In this case the short CrCr distance is most probably the result of the constraints imposed by the diazadiene ligand, implying a Cr2N4 core with a closer CrCr interaction.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-145697 (URN)10.1021/ic100345b (DOI)
Available from: 2011-02-10 Created: 2011-02-10 Last updated: 2017-12-11Bibliographically approved
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