Study of potential curves by UHF-type methods. Linearized coupled cluster methods with double substitution

Abstract

The potential energy curves have ben calculated for LiH, Li2, and N2 molecules by means of the L-CCD method (Linearized Coupled Cluster Method with Double Substitutions) based on the UHF and RHF reference functions. With each of the molecules, peculiarities are discussed of the description of the curves by the UHF-type methods on the basis of comparison with the full CI or experimental curves. The L-CCD(UHF) method gives a qualitatively correct course within the whole range of internuclear distances.