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Multireference (MR) configuration interaction (CI) approach for quasidegenerate systems
Author(s) -
Yamaguchi Kizashi
Publication year - 2009
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560180831
Subject(s) - configuration interaction , wave function , multireference configuration interaction , coupled cluster , atomic orbital , excited state , chemistry , atomic physics , valence (chemistry) , electronic correlation , full configuration interaction , molecular orbital , computational chemistry , physics , quantum mechanics , molecule , electron
The multireference (MR) configuration interaction (CI) wavefunctions utilizing generalized Hartree‐Fock (GHF) molecular orbitals are discussed in relation to our previous extended HF and recent full‐valence MCSCF methods for quasidegenerate systems. The reaction natural orbitals (RNO) for constructing the reference functions are selected on the basis of GHF calculations. The computational procedures for the MR CI are illustrated by considering imino nitroxide (HNNO) as an example. It is found that the present MR CI provides well‐balanced wavefunctions between the ground and lower‐lying excited states of the species. The correlation corrections coming from higher‐order excitations are examined by a Davidson‐like formula. The relation of this formula to the coupled‐cluster method is stressed.