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Perturbative ab initio calculations of intermolecular energies. II. The He ··· He problem
Author(s) -
Daudey J. P.,
Malrieu J. P.,
Rojas Olivia
Publication year - 1974
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560080103
Subject(s) - intermolecular force , van der waals force , basis (linear algebra) , ab initio , basis set , chemistry , electronic correlation , ground state , physics , atomic physics , statistical physics , quantum mechanics , thermodynamics , molecule , mathematics , geometry
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.