Overlap multipole moments

DMA = distributed multipole analysis ESP = electrostatic potential GAPT = generalized atomic polar tensor NAP = natural atomic population NMB = natural minimal basis NRB = natural Rydberg basis OMM = overlap multipole moments PEOE = partial equalization of orbital electronegativities RESP = restrained electrostatic potential. 

Schadler, G. H., 1992, Solution of Poisson s equation for arbitrary shaped overlapping or nonoverlapping charge densities in terms of multipole moments, PAy. Rev. 545 11314. 

The electrostatic interaction, which is defined as the classical Coulombic interaction between the undistorted charge distributions of the isolated molecules, is the easiest to derive from wavefunctions. When there is no overlap of the charge distributions of the molecules, all that is required is a representation of the molecular charge density. The traditional, and simplest, representation of the molecular charge distribution is in terms of the total multipole moments. The first nonvanishing multipole moment could often be derived from experi-... 

Atoms with closed subshells have no multipole moments and their electrostatic and induction interactions have a pure overlap origin from which follows their short-range character. The main contribution to Ef F gives the exchange interaction ch- Between atoms with closed subshells, it is repulsive (as in the noble-gas atom systems). This determines the unstability of the alkaline earth dimers at the SCF approximation. They are stabilized by the attractive electron correlation forces. 

The most important component of the water trimer nonadditive energy is the induction interaction of the second order in V. Its simple mechanism is shown in Fig. 33.3 a permanent multipole moment on monomer A induces multipole moments on monomer B which in turn interact with the permanent multipole moments of monomer C. Higher orders involve interactions between induced moments. The nonadditive induction energy is in general the most important nonadditive component for hydrogen-bonded systems. As already mentioned, it is the only term used—and only in the asymptotic approximation, i.e. neglecting charge-overlap effects—in the polarizable empirical potentials. 

Unfortunately this is still too severe a requirement in many cases. It is often possible for molecules to approach to distances at which such spheres would overlap, without encountering the repulsive part of the potential and even when they do not overlap, they may approach so closely that convergence becomes very slow. For this reason, it has become common to adopt a distributed multipole description, in which each molecule is divided into a number of regions, each described by its own multipole moments. There are many ways of determining these distributed multipole moments [6-11] many authors have used distributed charges alone, but it is now widely... 

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