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Degeneracy and coupled‐cluster approaches
Author(s) -
Paldus J.,
Takahashi M.,
Cho B. W. H.
Publication year - 1984
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.560260824
Subject(s) - degeneracy (biology) , degenerate energy levels , polyene , cluster (spacecraft) , coupled cluster , limit (mathematics) , statistical physics , physics , open shell , shell (structure) , theoretical physics , computational chemistry , computer science , quantum mechanics , chemistry , mathematics , materials science , bioinformatics , molecule , mathematical analysis , biology , programming language , organic chemistry , composite material
Problems which arise in the application of closed‐shell coupled‐cluster approaches to quasidegenerate or almost degenerate situations are discussed and the basic classification of quasidegeneracy types is outlined. Recent coupled‐cluster results obtained for the cyclic polyene model, particularly in the strongly correlated limit, are briefly discussed and the unexpected features of approximate and localized coupled‐pair approaches are pointed out.