J. Phys. II France
Volume 3, Numéro 11, November 1993
Page(s) 1593 - 1605
DOI: 10.1051/jp2:1993220
J. Phys. II France 3 (1993) 1593-1605

Order-by-order intermediate Hamiltonian expansions: applications to ab initio molecular calculations

A.V. Zaitsevskii

Laboratory of Molecular Structure and Quantum Mechanics, Chemical department, M. Lomonossov Moscow State University, 119899 Moscow, Russia

(Received 9 June 1993; accepted 23 July 1993)

A simple third-order intermediate Hamiltonian method based on the level shift technique is presented and applied to ab initio calculations on low-lying electronic states of CH +, CH 2+ and CH 2. The method is shown to provide a good approximation to full CI for both total energies and excitation energies. Numerous intruder states did not give rise to any instability problems. Series resummation using modified operator [2/1] Padé approximants and deviations of solutions by the present method from the strict size consistency are discussed.

03.65 - 31.15

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