First-principles phase diagram calculations for the system NaCl–KCl: The role of excess vibrational entropy

Abstract

First principles phase diagram calculations were performed for the system NaCl–KCl. Plane-wave pseudopotential calculations of formation energies were used as a basis for fitting cluster expansion Hamiltonians, both with and without an approximation for the excess vibrational entropy ( S VIB). Including S VIB dramatically improves the agreement between calculated and experimental phase diagrams: experimentally, the consolute point is { X C = 0.348, T C = 765 K} Exp; without S VIB, it is { X C = 0.46, T C ≈ 1630 K} Calc; with S VIB, it is { X C = 0.43, T C ≈ 930 K} Calc.