Premium
Applicability of quasi‐degenerate many‐body perturbation theory to quasi‐degenerate electronic states: The H 4 model revisited
Author(s) -
Mášsik Jozef,
Hubačc Ivan,
Mach Pavel
Publication year - 1995
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.560530207
Subject(s) - degenerate energy levels , degeneracy (biology) , perturbation theory (quantum mechanics) , excited state , perturbation (astronomy) , electronic correlation , quantum mechanics , physics , basis set , mathematical physics , molecule , bioinformatics , biology
The performance of the quasi‐degenerate many‐body perturbation theory up to the third order is investigated for the ground state, five excited states, and the first quintet of a simple four‐electron H 4 model system consisting of two stretched hydrogen molecules, in which the degree of quasi‐degeneracy can be continuously varied from a nondegenerate to a full degenerate situation. We employ a DZP basis set. The effect of intruder states is considered and a comparison with other multireference correlation techniques is also provided. Finally, a criterion for the model space to be quasi‐degenerate will be reformulated and generalized. © 1995 John Wiley & Sons, Inc.