An effective ion–ion potential for sodium

Abstract

The effective ion–ion interaction for sodium is calculated from a fundamental basis, using a one-orthogonalized plane wave (OPW) bare electron – ion matrix element, and the Geldart and Taylor electron gas screening function. Particular attention is paid to the form of the interaction for asymptotically large ion–ion separation, and it is shown that this interaction varies approximately as the fifth power of the ion–ion separation in the region in which the amplitude of the potential is appreciable. The elastic constants, cohesive energy, and the specific heats of body-centered cubic (b.c.c.) and close-packed sodium are shown to be in excellent agreement with experiment. The equilibrium and stability of the model sodium lattice described by the proposed potential are discussed, and it is concluded that the potential can be used tentatively in a fundamental calculation of atomic properties of defects.