CALCULATION OF THE 3-PARTICLE CONTRIBUTION TO THE CONFIGURATIONAL ENTROPY FOR 2 DIFFERENT MODELS OF AMORPHOUS SI

The two- and three-particle contributions to the configurational entropy (S2 and S3, respectively) were calculated by the method of Baranyai and Evans [Phys. Rev. A 42, 849 (1990)] for two different models of a-Si, obtained by reverse Monte Carlo simulations. The first model was the result of an unconstrained calculation, while the second one was obtained by using a constraint requiring 100% fourfold coordination. The pair-correlation functions of the two models were essentially the same, but cosine distributions of bond angles (a projection of the three-body correlation function) were remarkably different. Two-particle contributions to the configurational entropy do not differ for the two models. However, the difference in the three-particle contributions to the configurational entropy is large and the S3 of the 100% fourfold coordinated model is much more negative than that of the unconstrained model. This work is an attempt to make a quantitative distinction between structural models with identical pair-correlation functions.