A theoretical approach is presented that allows reproduction of the thermodynamic properties of anharmonic solids with low quantum coupling, such as solid argon, over the entire temperature range. The properties of the quantum system are obtained from classical Monte Carlo simulations by means of an effective potential which is based on a variational method developed recently. This technique is tested against extensive path-integral Monte Carlo calculations on a Lennard-Jones model of solid argon, and excellent agreement is found. It is also shown that the Lennard-Jones potential, with parameters derived from gas-phase data, provides a very good description of argon in the solid state.

• Received 15 April 1991

DOI:https://doi.org/10.1103/PhysRevB.45.2088