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  Efficient and accurate local single reference correlation methods for high-spin open-shell molecules using pair natural orbitals

Hansen, A., Liakos, D. G., & Neese, F. (2011). Efficient and accurate local single reference correlation methods for high-spin open-shell molecules using pair natural orbitals. The Journal of Chemical Physics, 135(21): 214102. doi:10.1063/1.3663855.

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Hansen, Andreas1, Author              
Liakos, Dimitrios G.1, Author              
Neese, Frank1, Author              
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1Research Department Neese, Max Planck Institute for Bioinorganic Chemistry, Max Planck Society, ou_3023879              

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 Abstract: A production level implementation of the high-spin open-shell (spin unrestricted) single reference coupled pair, quadratic configuration interaction and coupled cluster methods with up to doubly excited determinants in the framework of the local pair natural orbital (LPNO) concept is reported. This work is an extension of the closed-shell LPNO methods developed earlier [F. Neese, F. Wennmohs, and A. Hansen, J. Chem. Phys. 130, 114108 (2009) https://doi.org/10.1063/1.3086717.; F. Neese, A. Hansen, and D. G. Liakos, J. Chem. Phys. 131, 064103 (2009) https://doi.org/10.1063/1.3173827.]. The internal space is spanned by localized orbitals, while the external space for each electron pair is represented by a truncated PNO expansion. The laborious integral transformation associated with the large number of PNOs becomes feasible through the extensive use of density fitting (resolution of the identity (RI)) techniques. Technical complications arising for the open-shell case and the use of quasi-restricted orbitals for the construction of the reference determinant are discussed in detail. As in the closed-shell case, only three cutoff parameters control the average number of PNOs per electron pair, the size of the significant pair list, and the number of contributing auxiliary basis functions per PNO. The chosen threshold default values ensure robustness and the results of the parent canonical methods are reproduced to high accuracy. Comprehensive numerical tests on absolute and relative energies as well as timings consistently show that the outstanding performance of the LPNO methods carries over to the open-shell case with minor modifications. Finally, hyperfine couplings calculated with the variational LPNO-CEPA/1 method, for which a well-defined expectation value type density exists, indicate the great potential of the LPNO approach for the efficient calculation of molecular properties.

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Language(s): eng - English
 Dates: 2011-12-022011-12-07
 Publication Status: Published in print
 Pages: 20
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1063/1.3663855
 Degree: -

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Title: The Journal of Chemical Physics
  Abbreviation : J. Chem. Phys.
Source Genre: Journal
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Publ. Info: Woodbury, N.Y. : American Institute of Physics
Pages: - Volume / Issue: 135 (21) Sequence Number: 214102 Start / End Page: - Identifier: ISSN: 0021-9606
CoNE: https://pure.mpg.de/cone/journals/resource/954922836226