MONTE-CARLO SIMULATION OF THE EQUATION OF STATE OF HARD TETRAHEDRAL MOLECULES

The equation of state of a simple but rather general hard model for tetrahedral molecules at different densities and elongations is investigated through Monte Carlo simulation. Molecular volumes and surfaces as well as the second virial coefficients are also evaluated. This enables estimations of the anisotropic factor alpha. Nevertheless, semi-empirical pressures so obtained show only fair agreement with our pseudoexperimental data. Conversely, a very accurate equation-similar to that used by Tildesley and Streett for hard dumb-bells-is obtained by a nonlinear least squares fitting procedure. Interestingly, it requires only five parameters from which two are needed to reproduce the second virial coefficients. The parametrization makes available an accurate equation of state for a wide variety of hard tetrahedral systems which can be useful in perturbative approaches to real fluids.