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Perturbative ab initio calculations of intermolecular energies. I. Method

✍ Scribed by J. P. Daudey; P. Claverie; J. P. Malrieu

Publisher
John Wiley and Sons
Year
1974
Tongue
English
Weight
794 KB
Volume
8
Category
Article
ISSN
0020-7608

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✦ Synopsis

Abstract

Starting from a knowledge of approximate wave functions of the isolated molecules (or atoms) A and B, a method is proposed to build up a zeroth‐order ground state and excited configurations for the complex AB in which the molecular orbitals keep their local significance. The standard Rayleigh‐Schrödinger perturbation in this basis provides a decomposition of the zeroth‐order interaction energy as a sum of the electrostatic and repulsion energy. In the second order, it is possible to identify the classical dispersion and polarization forces (modified by a term of order S^2^) and two additional contributions which are linked to the exchange possibility. The intramolecular correlation component is taken into account and compared with the correlation on the isolated molecules. It is moreover suggested that since we work in a rather limited basis set, the perturbed energy of AB must be compared with the unperturbed energies of A and B calculated in a basis including the vacant orbitals on their respective partner. Finally a possibility for going beyond the second order is described.

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