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  A dynamic correlation dressed complete active space method: Theory, implementation, and preliminary applications

Pathak, S., Lang, L., & Neese, F. (2017). A dynamic correlation dressed complete active space method: Theory, implementation, and preliminary applications. The Journal of Chemical Physics, 147(23): 234109. doi:10.1063/1.5017942.

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 Creators:
Pathak, Shubhrodeep1, Author              
Lang, Lucas1, Author              
Neese, Frank1, Author              
Affiliations:
1Research Department Neese, Max Planck Institute for Chemical Energy Conversion, Max Planck Society, ou_3023886              

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 Abstract: Complete Active Space SCF (CASSCF) theory may provide poor 0th order descriptions due to the lack of dynamic correlation. The most popular post-CASSCF approaches for recovering dynamic correlation are methods which keep the configuration interaction coefficients fixed at the CASSCF level and use internal contraction. This may result in severe inaccuracies where the wavefunction changes considerably under the influence of dynamic correlation. In this paper, we propose and compare several variants of a straightforward method of the “perturb-then-diagonalize” type that is aimed at keeping this balance while remaining computationally tractable and numerically stable. The method is loosely based on the theory of intermediate Hamiltonians and has been given the acronym “dynamic correlation dressed CAS” (DCD-CAS), with the second-order treatment, DCD-CAS(2), being the most practically useful member of the family. The dynamic correlation energy is treated to second order with a 0th order Hamiltonian based on Dyall’s Hamiltonian. The method is orbitally invariant with respect to unitary transformations in the occupied, active, and virtual subspaces. It yields the ground- and low-lying excited states at the same time. Detailed numerical evaluations show that DCD-CAS(2) is superior to NEVPT2 for the difficult situations mentioned above while being very close to it when CASSCF provides a good 0th order description.

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Language(s): eng - English
 Dates: 2017-12-212017-12-21
 Publication Status: Published in print
 Pages: 17
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1063/1.5017942
 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: 147 (23) Sequence Number: 234109 Start / End Page: - Identifier: ISSN: 0021-9606
CoNE: https://pure.mpg.de/cone/journals/resource/954922836226