標題: Intruder States in Multireference Perturbation Theory: The Ground State of Manganese Dimer
作者: Camacho, Cristopher
Witek, Henryk A.
Yamamoto, Shigeyoshi
應用化學系
應用化學系分子科學碩博班
Department of Applied Chemistry
Institute of Molecular science
關鍵字: perturbation theory;intruder states;MCQDPT;CASPT2
公開日期: 1-二月-2009
摘要: A detailed analysis of a severe intruder state problem in the multistate multireference perturbation theory (MS-MRPT) calculations on the ground state of manganese dinner is presented. An enormous number of detected intruder states (> 5000) do not permit finding, even an approximate shape of the X(1) Sigma(+)(g) potential energy curve. The intruder states are explicitly demonstrated to originate from quasidegeneracies in the zeroth-order Hamiltonian spectrum. The electronic Configurations responsible for appearance of the quasidegeneracies are identified as single and double excitations from the active orbitals to the external orbitals. It is shown that the quasidegeneracy problem can be completely eliminated using shift techniques despite of its severity. The resultant curves are smooth and continuous. Unfortunately, strong dependence of the spectroscopic parameters of the X(1) Sigma(+)(g) state on the shift parameter is observed. This finding rises serious controversies regarding validity of employing shift techniques for solving the intruder state problem in MS-MRPT. Various alternative approaches of removing intruder states (e.g., modification of the basis set or changing the active space) arc tested. None of these conventional techniques is able to fully avoid the quasidegeneracies. We believe that the MS-MRPT calculations on the three lowest A(g) states of manganese dimer constitute a perfect benchmark case for studying the behavior of MRPT in extreme Situations. (C) 2008 Wiley Periodicals, Inc.
URI: http://dx.doi.org/10.1002/jcc.21074
http://hdl.handle.net/11536/7682
ISSN: 0192-8651
DOI: 10.1002/jcc.21074
期刊: JOURNAL OF COMPUTATIONAL CHEMISTRY
Volume: 30
Issue: 3
起始頁: 468
結束頁: 478
顯示於類別:期刊論文


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  1. 000262620800014.pdf