A Grand-Canonical Ensemble Monte Carlo study of the effects of change of core size on the thermodynamic properties of a modified Lennard-Jones fluid

It is shown by consideration of the fundamental theory that when dealing with potentials having hard cores the Grand Canonical Ensemble Monte Carlo (GCEMC) method should not introduce large errors of the type previously found in the use of the Shing-Gubbins (SG) method for estimation of the chemical potential. This is confirmed by making simulation runs using the GCEMC and the Canonical Ensemble Monte Carlo (CEMC) methods on similar systems having the hard-core Lennard-Jones intermolecular potential. Only when the hardcore parameter (alpha) (where the hard-core diameter is alpha sigma, sigma being the Lennard-Jones length parameter) is increased from 0.9 to 0.95 are appreciable changes in density and reduced potential energy (for a given mu) found. Corresponding, though much larger, changes in the fluctuations quantities f(NN)(= [N-2] - [N](2)) and f(NU)(= [NUN] -[N][U-N]), though not inf(NU)/f(NN), also occur.