Abstract
Equations of state (EOS) for a perfect solid and a perfect liquid are proposed, where the system includes only single spherical molecules. A Lennard-Jones interaction is assumed in the system. Molecular dynamics simulations are performed to obtain the temperature and density dependency of the internal energy and pressure. The internal energy in the EOS is the sum of the average kinetic energy and potential energy at 0 K, and the temperature dependent potential energy. The pressure is expressed in a similar way, where the pressure satisfies the thermodynamic EOS. The equilibrium condition is solved numerically for the phase equilibrium of argon. The Gibbs energy gives a reasonable transition pressure for 3-phase equilibrium in argon. The thermodynamic properties under low pressures have reasonable temperature dependences.
