First-principles calculation of L10-disorder phase diagram in Fe-Pt system within the first and second nearest neighbor pair interaction energies

FLAPW total energy calculations are performed for four kinds of ordered compounds in addition to pure Fe and pure Pt. Cluster expansion on the set of these total energies extracts effective nearest and second nearest neighbor pair interaction energies in-addition to multibody interaction energies up to regular tetrahedron interactions. The entropy term is evaluated within the Tetrahedron-Octahedron approximation of the Cluster Variation Method. Thereby, the second nearest neighbor pair interaction and correlation are fully taken into account in the resultant phase diagram. As compared with the phase diagram obtained previously within the nearest neighbor pair interaction, the transition temperature is raised. This is ascribed not only to the enhanced ordering tendency due to the second nearest neighbor pair interaction but also to the destabilization of a homogeneous solid solution. (C) 2003 Published by Elsevier Science Ltd.