Absolute entropy and free energy of fluids using the hypothetical scanning method.II.Transition probabilities from canonical MOnte Carlo simulations of partial systems

摘要

A variant of the hypothetical scanning (HS)method for calculating the absolute entroopy and free energy of fluids is developed,as applied to systems of Lennard-Jones atoms (liquid argon),As in the preceding paper (Paper I),a probability P_i approximating the Blotzmann probability of system configuration i,is calculated with a reconstruction procedure based on adding the atoms gradually to an initially empty volume,where they are placed in theri positions at i;in this process the volume is divided into cubic cells,which are visited layer-by-layer,line-by-line.At each step a transition probabilitky (TP)is calculated and the product of all the TPs leads to P_i.At step k,k-1 cells have already been treated,where among them N_k are occupied by a atom.A cononical metropolis Monte Carlo (MC) simulation is carried out over a portion of the still unvisited (future)volume thus providing an approximate representation of the N-N_k as yet untreated (future)atoms.The tp of target cell k is determined from the number of visits of future atoms to this cell during the simulation.This MC version of HS,called HSMC,is based o a relatively small number of efficiency parameters;their number does not grow and their values are not changed as the number of the treated future atoms is increased (i.e.,as the approximation improves);therefore,implementing HSMC for a relatively large number of future atoms (up to 40 in this study)is straightforward.Indeed,excellent results have been obtained for the free energy and the entropy.