Monte Carlo computer simulation of chain molecules. Part 6.—Interactions between n-alkane molecules

Abstract

The average intermolecular potential energy, ū₁₂, has been calculated for like-molecule pairs of methane, ethane, propane, n-butane and n-pentane. For a single pair of molecules the potential energy u₁₂ is assumed to be the sum of the atom–atom pair interactions. ū₁₂ is derived by averaging u₁₂ over molecular configurational states and orientations. The atom–atom pair interactions for CC, CH and HH were assumed to be given by the Buckingham potential. It was found that a value of the adjustable parameter b_CH(which characterises the repulsion energy between the unlike atom pair) equal to 0.936 of the geometric mean value produced reasonably good agreement between the calculated and the experimental second virial coefficients for all the systems over a wide range of temperature. The computed u₁₂(r) functions were found to be temperature-dependent, and they do not conform to either the Buckingham or the Lennard-Jones forms of the potential functions.