THERMODYNAMIC PROPERTIES OF SOLID AR, KR, AND XE BASED UPON A SHORT-RANGE CENTRAL FORCE AND CONVENTIONAL PERTURBATION EXPANSION OF PARTITION FUNCTION

Thermodynamic properties of the rare-gas solids Ar, Kr, and Xe are calculated using phenomenological two-body central potentials. The cubic and quartic anharmonic terms in the crystal Hamiltonian have been included, using conventional perturbation theory. Although some definite discrepancies with experiment exist for T<13Tmelting these simple models give a fair over-all account of both the volume and temperature dependence of the Helmholtz energy. However, for T>13Tmelting (rms deviations greater than ∼6% of the nearest-neighbor distance), anharmonic contributions to the thermodynamic properties become unrealistically large, indicating, we believe, the breakdown of perturbation theory to the order considered in this work. © 1969 The American Physical Society.