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  Approximations of density matrices in N-electron valence state second-order perturbation theory (NEVPT2). II. The full rank NEVPT2 (FR-NEVPT2) formulation

Guo, Y., Sivalingam, K., Kollmar, C., & Neese, F. (2021). Approximations of density matrices in N-electron valence state second-order perturbation theory (NEVPT2). II. The full rank NEVPT2 (FR-NEVPT2) formulation. The Journal of Chemical Physics, 154(21): 214113. doi:10.1063/5.0051218.

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5rdm-si-210226.pdf (Supplementary material), 257KB
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 Creators:
Guo, Yang1, Author              
Sivalingam, Kantharuban2, Author              
Kollmar, Christian3, Author              
Neese, Frank3, Author              
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1Qingdao Institute for Theoretical and Computational Sciences, Shandong University, Qingdao, Shandong 266237, China, ou_persistent22              
2Research Group Wennmohs, Max-Planck-Institut für Kohlenforschung, Max Planck Society, ou_2541706              
3Research Department Neese, Max-Planck-Institut für Kohlenforschung, Max Planck Society, ou_2541710              

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 Abstract: In Paper I, the performances of pre-screening (PS), extended PS (EPS), and cumulant (CU) approximations to the fourth-order density matrix were examined in the context of second-order N-electron valence state perturbation theory (NEVPT2). It has been found that the CU, PS, and even EPS approximations with loose thresholds may introduce intruder states. In the present work, the origin of these “false intruder” states introduced by approximated density matrices is discussed. Canonical NEVPT2 implementations employ a rank reduction trick. By analyzing its residual error, we find that the omission of the rank reduction leads to a more stable multireference perturbation theory for incomplete active space reference wave functions. Such a full rank (FR)-NEVPT2 formulation is equivalent to the conventional NEVPT2 method for the complete active space self-consistent field/complete active space configuration interaction reference wave function. A major drawback of the FR-NEVPT2 formulation is the necessity of the fifth-order density matrix. To avoid the construction of the high-order density matrices, the combination of the FR-NEVPT2 with the CU approximation is studied. However, we find that the CU approximation remains problematic as it still introduces intruder states. The question of how to robustly and efficiently perform internally contracted multireference perturbation theories with approximate densities remains a challenging field of investigation.

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Language(s): eng - English
 Dates: 2021-03-232021-05-092021-06-042021-06-07
 Publication Status: Published in print
 Pages: 11
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1063/5.0051218
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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: 154 (21) Sequence Number: 214113 Start / End Page: - Identifier: ISSN: 0021-9606
CoNE: https://pure.mpg.de/cone/journals/resource/954922836226