Entropy of liquid alkali metals studied by the correlation expansion method

We investigate the temperature-dependences of the entropies of liquid alkali metals using a correlation expansion scheme with the computer-simulated pair correlation functions as sole input data. It was found that the ensemble invariant or the local form entropy formula is an appropriate and practical expression to use in numerical study of entropy. Our results show that it is now possible to understand the contradictory trend found between the excess entropy and the static liquid structure factor S(q) in the application of the thermodynamic perturbative or variational theory. Numerically the predicted values are fairly accurate near the freezing temperature of all four liquid alkali metals but they begin to deteriorate at higher temperatures. The implication is that at high temperatures the density fluctuation effects in the small q region of S(q) become dominant and, as shown in present work, play a non-negligible role in the entropy calculation.