Straightforward calculation of the WCA entropy and internal energy for liquid metals

The explicit expression for the reference-system entropy within the Weeks–Chandler–Andersen (WCA) approximation is derived and applied to straightforward calculation of the WCA entropy and internal energy of liquid alkali metals. It is shown that the procedure used gives the same results as a numerical differentiation of the Helmholtz free energy but with a smaller computing complexity.

► The WCA reference system for a soft-core pair potential is studied.
► Explicit expressions for the WCA entropy and internal energy are obtained.
► Numerical calculations for liquid Na, K, Rb, and Cs are fulfilled.