Structural modelling of fluid ethane with Monte Carlo methods

Abstract

Recently determined neutron diffraction results for fluid ethane at T=370 K and four densities were fitted with Reverse Monte Carlo simulations. In addition, Monte Carlo simulations in the NVT-ensemble were performed with an empirically deduced effective eight-site pair potential. The experimentally determined total atom pair correlation functions were well reproduced. The individual atom pair correlation functions calculated with Monte Carlo and Reverse Monte Carlo agree very well and show a pronounced fine-structure and a significant density effect. The final configurations were used to calculate angular distribution functions that show a disordered arrangement of the molecules with respect to their centers, but high angle correlations for the nearest neighbour interactions compared to a statistically disordered model system. The center–center correlation functions for four special molecule-pair orientations (crossed, T-shaped, parallel adjacent and parallel end-to-end) show an increased occurrence of molecular orientations at distances that correlate with the minima positions in the corresponding potential energy curves for these orientations. The atom pair correlations functions for these four special species show that the orientational short range order causes the fine structure in the atom pair correlation functions.