Comparison of polarizable and nonpolarizable models of hydrogen fluoride in liquid and supercritical states: A Monte Carlo simulation study

Structural and thermodynamic properties of a polarizable and two pairwise a dditive effective interaction potential models of hydrogen fluoride are ana lyzed and compared with experimental data in the liquid and supercritical p hase as well as along the vapor-liquid coexistence line. Pair correlation f unctions and thermodynamic data are obtained from Monte Carlo simulations a t two liquid and four supercritical thermodynamic state points. Vapor-liqui d equilibrium properties have been calculated from a set of Gibbs ensemble Monte Carlo simulations. It is found that the polarizable model is clearly superior over the two nonpolarizable ones in describing the temperature and density variation of several thermodynamic and structural properties. Thus the experimentally observed elongation of the hydrogen bonds with decreasi ng density is only reproduced by the polarizable model. Similarly, among th e three models only the polarizable one can correctly describe the dependen ce of the density on the pressure and temperature in the entire range of th e liquid state, although the density of this model is always somewhat lower than that of real HF. Consistently, the vapor-liquid coexistence curve is also much better reproduced by the polarizable than by the other two models . All three models underestimate the critical temperature, although the pol arizable model is again in a considerably better agreement with the experim ental data than the other two. All three models reproduce the experimental fact that the energy of evaporation of HF goes through a maximum as a funct ion of the temperature. (C) 2001 American Institute of Physics.