For the simple alkali halide ionic system there are only two ionic radii: , so it is useful to consider their sum and their reduced difference . In this study, we focus our attention on the influence of the size mismatch of δ on the thermodynamics of melting, assuming the influence of parameter d to be more obvious. This model system can serve as a purely theoretical example of classical ionic system with arbitrary parameters of the Born repulsion. Let us consider the influence of both parameters in the expression (2) on the pair potential energy curve. Fig. 1 illustrates regular changes in shape in the case of unlike ions. Namely, well location depending more strongly on the scale parameter (a) and the curvature determined by ρ.