On the calculation of the chemical potential using the particle deletion scheme

Abstract

A new formulation is presented for the calculation of the chemical potential from molecular simulation based on a test particle removal (inverse Widom) scheme. The new formulation introduces an intermediate stage in the calculation where the test particle to be removed is substituted by a hard particle. Chemical potential calculations at high densities from NVT and NPT Monte Carlo simulations, using a fast analytical algorithm for the computation of volume accessible to the hard core particle, are presented for the pure Lennard-Jones fluid and found to be in excellent agreement with predictions from an accurate equation of state and from simulations using the test particle insertion scheme (Widom insertion scheme). Binary mixture simulations are presented also and the new scheme is applied in the Gibbs ensemble. In all cases where the system is highly dense, the new inverse Widom scheme affords a significant reduction in CPU time compared with the widely used test particle insertion method of Widom. In addition, the new scheme is compared with a recently proposed scheme based on staged insertion.