Ab Initio Study of Phase Equilibria in [Formula presented]

Abstract

The phase diagram for the vacancy-ordered structures in the substoichiometric [Formula presented] ([Formula presented]) has been established from Monte Carlo simulations with the long-range pair and multisite effective interactions obtained from ab initio calculations. Three ordered superstructures of vacancies ([Formula presented], [Formula presented], and [Formula presented]) are found to be ground state configurations. Their stability has been verified by full-potential total energy calculations of the fully relaxed structures. © 2002 The American Physical Society.