Hartree–Fock approximate correlation energy (HFACE) potential for diatomic interactions. Molecules and van der Waals molecules

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Abstract
A model potential function recently developed for van der Waals molecules has been extended to bound-state diatomics. It is written as the sum of the (extended) Hartree–Fock energy and the (remaining) correlation energy, each of these being elaborated separately from available data pertaining to the regions of the potential where they stand as the dominant energy contributions. The correlation energy is approximated semiempirically from the asymptotic expansion for the dispersion energy, the terms of which are individually damped to account for charge overlap and exchange effects. To determine the values of the C8 and C10 dispersion coefficients, which are missing in the literature, it is proposed the semiempirical rule Cn/C6=knR[a(n–6)/2] 0, which is believed to be accurate within 15% for C8 and 30% for C10. Results are presented for thirteen chemically stable bound-state diatomics, in addition to three van der Waals molecules which are typical members of as many families of non-bonding interactions: the ground state of the rare-gas dimers and the alkali earth dimers, and the lowest triplet state of the alkali-metal dimers. The results are all good.

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