A new method for the calculation of dispersion energies. Application of alkali-rare-gas interactions

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Abstract
Following a basic idea formulated by Bottcher and Dalgarno (1974), a non-symmetrical method is proposed for the calculation of the dispersion energy between a versatile system A (treated in a large basis set) and a quasi-passive system B (treated through a frozen electronic description and characterised by its polarisability). After a (A+frozen B) SCF+CI calculation the method only requires the calculation of the electric field created by A on B and the fluctuation of this electric field. An effective Hamiltonian version of the method is proposed. The method has been applied to the lowest potential curves of argon-Na, K diatoms, dissociating into the ns, np, (n+1)s, (n+1)p and 3d atomic states of the alkali atom. Good agreement is obtained with previous calculations and experiment when available. The features of the excited-state potential curves are interpreted in terms of overlap (i.e. repulsion) minimising hybridisation.

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