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 under standing the changes in vibrational properties that result from disordering . In the present work the effects of local environments on thermodynamic qu antities are examined using the embedded-atom method (EAM) for Ni3Al and Cu 3Au. Projections of the density of states onto different local environments are performed, and a local cluster expansion is calculated. It is found th at the contribution to the entropy from a given atom is primarily determine d by the atom and its first few neighbor shells. Relaxations are seen to qu alitatively change the dependence of the entropy on local environment, chan ging the sign of the dominant interactions, Also, relaxations are found to extend the range of point and pair interactions and to increase the importa nce of multisite interactions. These results suggest that a special quasi-r andom structure (SQS), a small supercell constructed to approximate the loc al environments of the disordered phase, might be able to reproduce the dis ordered phase vibrational thermodynamics. It is found that an eight-atom SQ S can accurately represent the vibrational thermodynamic properties of the disordered phase, implying that it could be a powerful tool for first princ iples vibrational studies.