Abstract
An equation of state for a perfect solid is proposed, where the system includes only single spherical molecules. A Lennard-Jones interaction is assumed in the nearest neighbors on the face-centered cubic (FCC) lattice. The internal energy is the sum of the average kinetic energy and the potential energy at 0 K, which is a function of the volume. The pressure satisfies the thermodynamic conditions for the internal energy and pressure. The equilibrium condition is solved numerically for the solid-gas equilibrium of argon. The Gibbs energy gives a reasonable vapor pressure for solid argon, if the temperature dependence of the virial term is taken into account.
