Calculation of entropy with computer simulation methods

A new approximate method for calculating entropy with computer simulation methods is proposed. The sampling probability of an equilibrium configuration is calculated by means of the frequency of occurrence of what we call here local states (related to the state of the particle and its neighbors); hence entropy can be calculated as well. The method is applied to the Metropolis' Monte Carlo simulation for the case of the square Ising lattice. The results are in very good agreement with theory even close to the critical temperature. The method is used also to calculate non-equilibrium entropy.