Four Important Factors in the ab initio Determination of Accurate Inter-Ionic Potentials

Abstract

Abstract The accurate ab initio determination of inter-ionic potentials requires the consideration of four important factors. These are relativistic effects for ions of high atomic number, the environmentally induced modifications of ion wavefunctions, the damping of reliably calculated inter-ionic dispersive attractions and the avoidance of density functional descriptions of the uncorrelated potentials. The relativistic modifications of the behaviour of valence electrons in elements heavier than those of the third series of transition elements are too large to be treated by first order perturbation theory. The relativistic integrals programme (RIP), which works directly with the Dirac equation and four component wavefunctions for the individual electrons, is used to compute fully relativistic inter-ionic potentials. The mechanisms through which ion wavefunctions are modified by their environment in the crystal are discussed. A simple yet physically realistic model for computing such wavefunctions is pres...