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Intermolecular interactions in the region of small overlap
Author(s) -
Basilevsky M. V.,
Berenfeld M. M.
Publication year - 1972
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.560060103
Subject(s) - feynman diagram , hamiltonian (control theory) , quantum mechanics , wave function , antisymmetry , orthogonalization , multipole expansion , basis (linear algebra) , physics , fock space , statistical physics , mathematics , geometry , mathematical optimization , linguistics , philosophy
In order to treat the interaction energy of two molecules a standard Rayleigh‐Schrödinger perturbation theory is developed. The Hartree–Fock functions of the separated molecules are used as one particle basis functions, the initial set of states being truncated and non‐orthogonal. The non‐orthogonality is included into the Hamiltonian by orthogonalization of the basis set. The unperturbed Hamiltonian is chosen so that it possesses the correct symmetry properties with respect to the electron permutations between different molecules. The procedure of this kind automatically results in the appearance of charge transfer states. A graphical technique is elaborated which is a modified version of the Feynman–Goldstone technique and provides a convenient representation of the interaction energy contributions of any order. As an example the first‐ and the second‐order diagrams are considered. A correct expression for the dispersion energy is obtained which differs by a factor from that of the theory using a nonsymmetrical zero approximation.