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. ZaitsevskiiLaboratory of Molecular Structure and Quantum Mechanics, Chemical department, M. Lomonossov Moscow State University, 119899 Moscow, Russia
(Received 9 June 1993; accepted 23 July 1993)
Abstract
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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