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COUPLED-CLUSTERANDCONFIGURATION-INTERACTION APPROACHES TO QUASIDEGENERACY

  • JOSEF PALDUS
  • XIANGZHU LI
Conference paper
Part of the Progress in Theoretical Chemistry and Physics book series (PTCP, volume 15)

Abstract

The capability of the variational and perturbative-type approaches to the many-electron correlation problem – as represented by the configuration interaction (CI) and coupled cluster (CC) theories – to describe, respectively, the nondynamic and dynamic correlation effects, is emphasized, and its exploitation in the design of the so-called externally corrected CC methods, as well as in the formulation of Davidson-type corrections that are based on the CC theory, at both single reference and multireference levels, is reviewed. The performance of various methods of this type is illustrated on the DZP H4 model that consists of two interacting and slightly stretched hydrogen molecules in a trapezoidal geometry. This often studied model enables a continuous transition from the degenerate to the nondegenerate regime by varying the degree of quasidegeneracy via a single geometric parameter. In this way the role of higher-than-pair clusters, particularly in the presence of intruder states, can be explored and the performance of various approaches that exploit the complementarity of the CI and CC approaches can be evaluated.

Keywords

State Universal Intruder State CCSD Method Cluster Amplitude Nondynamic Correlation 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer 2006

Authors and Affiliations

  • JOSEF PALDUS
    • 1
    • 2
  • XIANGZHU LI
    • 3
  1. 1.Department of Applied MathematicsUniversity of WaterlooOntarioCanada
  2. 2.Department of Chemistry and Guelph-Waterloo Center for Graduate Work in Chemistry, Waterloo CampusUniversity of WaterlooOntarioCanada
  3. 3.Department of Applied MathematicsUniversity of WaterlooOntarioCanada

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