Three-particle contribution to the configurational entropy of simple fluids

Abstract

We report a molecular-dynamics calculation of the entropy of a simple, classical fluid. The two- and three-body contributions to the total entropy were calculated from an expansion recently derived by the present authors [Phys. Rev. A 40, 3817 (1989)]. Both the two- and three-particle contributions to the entropy are monotonically decreasing functions of density at a fixed temperature. The two-body term remains less negative than the excess entropy over the entire fluid range with the largest discrepancy, of ∼15%, occurring at intermediate densities. The sum of the two- and three-body terms gives an accurate estimate of the excess entropy at low and intermediate densities. At intermediate densities the sum crosses the value of the total excess entropy and at still higher densities, close to the freezing line, becomes somewhat more negative (∼30%) than the total excess entropy. These results show that the expansion of the entropy converges less rapidly than might have been assumed from an analysis of the two-body terms alone.