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Analytical gradients of the state-average complete active space self-consistent field method with density fitting
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
University of Oslo.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry. Università di Bologna.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
2015 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 143, no 4, article id 044110Article in journal (Refereed) Published
Abstract [en]

An efficient implementation of the state-averaged complete active space self-consistent field (SA-CASSCF) gradients employing density fitting (DF) is presented. The DF allows a reduction both in scaling and prefactors of the different steps involved. The performance of the algorithm is demonstrated on a set of molecules ranging up to an iron-Heme b complex which with its 79 atoms and 811 basis functions is to our knowledge the largest SA-CASSCF gradient computed. For smaller systems where the conventional code could still be used as a reference, both the linear response calculation and the gradient formation showed a clear timing reduction and the overall cost of a geometry optimization is typically reduced by more than one order of magnitude while the accuracy loss is negligible.

Place, publisher, year, edition, pages
2015. Vol. 143, no 4, article id 044110
National Category
Theoretical Chemistry
Research subject
Chemistry with specialization in Quantum Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-243572DOI: 10.1063/1.4927228ISI: 000358929100016PubMedID: 26233110OAI: oai:DiVA.org:uu-243572DiVA, id: diva2:787590
Funder
Swedish Research CouncileSSENCE - An eScience CollaborationAvailable from: 2015-02-10 Created: 2015-02-10 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Extending the Reach of Accurate Wavefunction Methods
Open this publication in new window or tab >>Extending the Reach of Accurate Wavefunction Methods
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Multiconfigurational quantum chemistry methods, and especially the multiconfigurational self-consistent field (MCSCF) and multireference perturbation theory (MRPT2), are powerful tools, particularly suited to the accurate modeling of photochemical processes and transition metal catalysis. However, they are limited by their high computational cost compared to other methods, especially density functional theory. Moreover, there are areas where they would be expected to perform well, but where they are not applied due to lack of experience.

This thesis addresses those issues. First, the efficiency of the Cholesky decomposition approximation to reduce the cost of MCSCF and MRPT2 without sacrificing their accuracy is demonstrated. This then motivates the extension of the Cholesky approximation to the computation of MCSCF nuclear gradients, thus strongly improving the ability to perform MCSCF non-adiabatic molecular dynamics. Typically, a tenfold speed-up is observed allowing dynamic simulation of larger systems or over longer times.

Finally, multiconfigurational methods are applied to the computation of X-ray spectra of transition metal complexes. The importance of the different parameters in the calculation is systematically investigated, laying the base for wider applications of those accurate methods in the modeling of X-ray spectroscopy. A tool to analyze the resulting spectrum in terms of molecular orbitals is also presented, strengthening the interplay between theory and experiments.

With these developments and other significant ones that have happened in recent years, multiconfigurational methods can now reach new grounds and contribute to important new discoveries

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. p. 75
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1228
Keywords
Quantum chemistry, Density fitting, CASSCF, Analytical gradients, Photochemistry, X-ray spectroscopy
National Category
Theoretical Chemistry
Research subject
Chemistry with specialization in Quantum Chemistry
Identifiers
urn:nbn:se:uu:diva-243573 (URN)978-91-554-9168-0 (ISBN)
Public defence
2015-03-31, Siegbahnsalen, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2015-03-10 Created: 2015-02-10 Last updated: 2015-04-14Bibliographically approved

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Delcey, Mickaël G.Lindh, Roland

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