Lattice Dynamics with Three-Body Forces: Argon

Abstract

The specific heat, thermal expansion, and bulk modulus of crystalline argon at low temperatures (up to 12 \ifmmode^\circ\else\textdegree\fi{}K) are calculated using pair potential functions known to be consistent with pair-interaction data, together with the Axilrod-Teller triple-dipole interaction. The methods of lattice dynamics are used and correction for anharmonicity is made. The potential of Barker and Pompe gives good agreement with experimental specific heats and a slight modification of this potential gives excellent agreement. The modified potential also gives excellent agreement with experimental thermal-expansion results, but the calculated bulk modulus is about 9% higher than current experimental estimates. Harmonic calculations are also made using the potential of Dymond and Alder. The resulting harmonic specific heats are in very poor agreement with experiment and there are very large anharmonic effects.