Local environment effects in the vibrational properties of disordered alloys: An embedded-atom method study of Ni₃Al and Cu₃Au

Local environment effects are important for providing a framework for understanding the changes in vibrational properties that result from disordering. In the present work the effects of local environments on thermodynamic quantities are examined using the embedded-atom method (EAM) for Ni3Al and Cu3Au. Projections of the density of states onto different local environments are performed, and a local cluster expansion is calculated. It is found that the contribution to the entropy from a given atom is primarily determined by the atom and its first few neighbor shells. Relaxations are seen to qualitatively change the dependence of the entropy on local environment, changing the sign of the dominant interactions, Also, relaxations are found to extend the range of point and pair interactions and to increase the importance of multisite interactions. These results suggest that a special quasi-random structure (SQS), a small supercell constructed to approximate the local environments of the disordered phase, might be able to reproduce the disordered phase vibrational thermodynamics. It is found that an eight-atom SQS can accurately represent the vibrational thermodynamic properties of the disordered phase, implying that it could be a powerful tool for first principles vibrational studies.