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Perturbative ab initio calculations of intermolecular energies. II. The He ··· He problem

✍ Scribed by J. P. Daudey; J. P. Malrieu; Olivia Rojas

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

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✦ Synopsis

Abstract

The ground state energy of the He~2~ system is calculated according to the techniques described in Paper I around the van der Waals equilibrium, without assuming the constancy of the intraatomic correlation energies. The second‐order results do not present an attractive region; the S^2^ decrease of the intraatomic correlation correlation corrections is larger than the attractive interatomic correlation corrections. The further orders reverse progressively the situation and finally give a qualitatively correct potential curve after the fifth order. Reaching almost exact solutions in the considered basis, one can demonstrate that the intermolecular calculation of the system A + B in the union of the basis for A and B involves an energy decrease which simply represents the effect of the extension of the basis set; and that a proper intermolecular calculation must compare the A + B energy with the A and B energies calculated in conveniently extended basis sets including the vacant MO's of the partner.

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