Study of localized molecular orbitals using group theory methods and its approach to the many-electron correlation problem. III. Orthogonal bonded functions

1993 ◽  
Vol 14 (5) ◽  
pp. 549-555 ◽  
Author(s):  
Taijin Zhou
Keyword(s):  
Group Theory ◽  
Electron Correlation ◽  
Molecular Orbitals ◽  
Localized Molecular Orbitals ◽  
Correlation Problem ◽  
The Many

Coupled-pair theories and Davidson-type corrections for quasidegenerate states: The H4 model revisited

1988 ◽  
Vol 53 (9) ◽  
pp. 1919-1942 ◽  
Author(s):  
Josef Paldus ◽  
Paul E. S. Wormer ◽  
Marc Benard
Keyword(s):  
Electron Correlation ◽  
Model System ◽  
Coupled Cluster ◽  
Electron Model ◽  
Hydrogen Molecules ◽  
Double Zeta ◽  
Correlation Problem ◽  
Variational Approaches ◽  
Cluster Type ◽  
The Many

The performance of various variational and non-variational approaches to the many-electron correlation problem is examined for a simple four-electron model system consisting of two stretched hydrogen molecules in trapezoidal, rectangular and linear configurations, in which the degree of quasi-degeneracy can be continuously varied from a non-degenerate to an almost degenerate situation. In contrast to an earlier work (K. Jankowski and J. Paldus, Int. J. Quantum Chem. 18, 1243 (1980)) we employ a double-zeta plus polarization basis and examine both single reference and multireference configuration interaction and coupled-cluster-type approaches. The performance of various Davidson-type corrections is also investigated.

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