Search

In this paper, we present a method for the calculation of dispersion interaction energies of molecules, which is based on the localized molecular orbitals of the supermolecule. It is shown (using various basis sets) that the energy contributions of the localized molecular orbitals, for distances around the intermolecular energy minimum, are transferable to a fairly good approximation from the noninteracting monomers to the supermolecule. The correlation energy component of the interaction energy can be separated into inter‐ and intraparts. We show how the basis set superposition errors can be located and separated at the correlated level. Results are presented for several systems [(H2O)2, (NH3)2, and Ne2 ] with different basis sets from the minimal one to the split shell plus polarization functions. The method applies the well‐known Boys’ localization procedure and has the advantage that for the dispersion energy at a given geometry, the integral transformation should only be carried out once (from the ba...

Assuming that truncated strongly orthogonal geminals for a system are already known, the possibility of using rij‐dependent correction functions in the geminals is discussed with an emphasis on the violation of the strong orthogonality conditions. It is shown that for given truncated geminals there always exists at least one optimally decomposed complete set of one‐electron functions, which makes it possible to pick out the configurations giving rise to strong orthogonality condition violating terms in the energy expression. The latter can be neglected, as compared with others which are of second order in the correction functions, when the system consists of spatially separated pairs in the sense that the one‐electron functions contributing appreciably to one pair do not have significant differential overlap with the starting basis functions of other pairs. In this case interorbital effects are also small. For systems consisting of weakly localizable pairs, when the strong orthogonality condition violatin...