Theoretical Equation of State for Highly Anharmonic Solids

Thermodynamic properties of Lennard–Jones (LJ) face-centered cubic crystals are calculated in a wide range of temperatures along sublimation and melting lines on the basis of statistical mechanical theory which accounts for anharmonicity, pair and triple correlations in the displacements of atoms. Results are compared with the most accurate Monte Carlo data available. Excellent agreement was found. Anharmonic and correlation contributions to entropy, internal energy, and the compressibility factor of LJ solids are computed and their relative importance analyzed. An analytical equation of state approximating the theoretical results is developed.