van der Waals forces in a Monte Carlo and lattice-dynamics study of the thermal and elastic properties of a rigid-ion model of potassium chloride

We present benchmark calculations of the thermodynamic and elastic properties of a rigid-ion model of potassium chloride, at zero pressure, using a combination of Monte Carlo simulation at high temperatures (300--1000 K) and anharmonic lattice dynamics at low temperature (0--300 K). A new feature of our results is the fact that excellent agreement with the experimental results requires that, in contrast to the case of sodium chloride, the Born-Mayer repulsive interaction between nearest and third-nearest neighbors be supplemented by an attractive van der Waals interaction between second neighbors. We briefly discuss the problem of three-body forces.