(253aa) Computation of Chemical Potential of Water at Low Temperatures

Calculations of free energy changes and chemical potentials are of great importance in chemical engineering. In this work, the performance of the Gibbs ensemble combined with Continuous Fractional Component method (GE-CFCMC) for free energy calculation in dense systems has been compared to the Widom test particle insertion in the conventional Gibbs ensemble. For this study, 3 different water models have been considered: TiP3P-EW, TiP4P-EW, SPC. It is shown that while Widom test particle method fails to provide a correct estimation of the chemical potential for the liquid phase at low temperatures, the simulations using GE-CFCMC can estimate chemical potential correctly. It is also shown that the acceptance probability for the particle exchange between the boxes has been improved using the GE-CFCMC method by Poursaeidesfahani et al. [Direct Free Energy Calculation in the Continuous Fractional Component Gibbs Ensemble, Journal of Chemical Theory and Computation, 2016, 12 (4), pp 1481â??1490]. The GE-CFCMC method has eliminated one of the coupled fractional particles in one of the boxes and therefore, operates only with a single fractional particle in one of the boxes at a time. Therefore, especially when the fractional particle is in the gas phase, the pair potential calculations in the liquid phase are no longer needed. This reduces the computational time significantly.