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Hylleraas Variational Perturbation Theory: Application To Correlation Problems In Molecular Systems, Robert J. Cave, Ernest R. Davidson

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Hylleraas variational perturbation theory is applied through second order in energy to estimate the correlation energy in several molecular systems. The specific choices for H₀ and V which are made lead to equations nearly identical to the multireference linearized coupled‐cluster method of Laidig and Bartlett. The results obtained are in virtually exact agreement where comparisons have been made. Results from test calculations are presented for BeH₂, CH₂, and C₂H₄. In addition, the utility of perturbation theory for selecting correlating configurations is examined. This procedure is found to be quite accurate while …