Distributed electrostatic moments based

Distributed Electrostatic Moments Based on the Electron Localization Function Partition... 

That way, the Distributed Electrostatic Moments based on the ELF Partition (DE-MEP) allows computing of local moments located at non-atomic centres such as lone pairs, a bonds and n systems. Local dipole contributions have been shown to be useful to rationalize inductive polarization effects and typical hydrogen bond interactions. Moreover, bond quadrupole polarization moments being related to a n character enable to discuss bond multiplicities, and to sort families of molecules according to their bond order. 

In the derivation of the traceless quadrupole moments from the electrostatic moments, the spherical components are subtracted. Thus, the quadrupole moments can be derived from the second moments, but the opposite is not the case. Spackman (1992) notes that the subtraction introduces an ambiguity in the comparison of quadrupole moments from theory and experiment. The spherical component subtracted is not that of the promolecule, but is based on the distribution itself. It is therefore generally not the same in the two densities being compared. On the other hand, the moments as defined by Eq. (7.1) are based on the total density without the intrusion of a reference state. 

An alternative approach was to include explicit, higher order electrostatic moments in the pairwise interactions. This approach has not been extensively developed for use in molecular simulations because of the complex set of moments needed to obtain sensible results, particularly to mimic hydrogen bonding. A notable exception is the polarizable electropole model, which relies on a central polarizability as well as higher order moments to capture the electrostatic part of the interactions." The computational effort required for a multipole-based representation of the electrostatics is much greater than is involved in the use of distributed charges to represent the electrostatic interactions. If, on the other hand, the number of partial charge sites is substantially increased, a local expansion of multipole moments can become computationally economical. ... 

The pioneering finite temperature Monte Carlo study [282] of the orientational disordering of commensurate and incommensurate monolayers of CO on graphite was based on empirical potentials and 64 molecules in a rectangular periodic cell. The CO-surface interactions were modeled with the Fourier representation [324, 326], and the necessary Lennard-Jones parameters were obtained from a fit to the measured isosteric heats of adsorption [287]. The nonelectrostatic CO-CO intermolecular interactions were based on Buckingham-type potentials as parameterized in Refs. 238 and 287. The electrostatics was represented by a three-site point-charge distribution located on the molecular axis [282]. The chosen values yield a reasonable representation of the moments up to the hexadecapole the dipole moment, however, is larger than the experimental value. These interactions... 

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