Continuous charge distribution models of ions in polar media. Part 1

Abstract

In this paper we discuss a number of charge distribution models of ions in polar solution. In particular, we examine models based on Born, Slater and gaussian charge distribution as well as some combinations of these charge distributions. Self and interaction energy quantities are derived for the various ionic models. In addition, self energies are calculated for some typical examples. The self and interaction energies are of particular importance in connexion with the electron transfer process. One object of this work is the search for relatively simple and accurate charge distribution representations which take account of the major physical and chemical characteristics of ionic systems. Our investigations indicate that the gaussian distribution gives the best overall representation. This is a great advantage, as the gaussian representation of an ionic charge system is the simplest mathematically. Specifically, we find that for cations a double charge distribution works well. The ionic radius marks the region of maximum positive charge density (including the uncovered positive core charge due to subvalence electronic delocalization). A second quantity, an effective Bohr radius which corresponds to the Glueckauf radius, marks the region of maximum delocalized subvalence electronic charge. For anions we find that the atomic instead of the ionic radii give the best results with the use only of a single soft charge representation.