Using bond-length-dependent transferable force constants to predict vibrational entropies in Au-Cu, Au-Pd, and Cu-Pd alloys

A model is tested to rapidly evaluate the vibrational properties of alloys with site disorder. It is shown that length-dependent transferable force constants exist and can be used to accurately predict the vibrational entropy of substitutionally ordered and disordered structures in Au-Cu, Au-Pd, and Cu-Pd. For each relevant force constant, a length-dependent function is determined and fitted to force constants obtained from first-principles pseudopotential calculations. We show that these transferable force constants can accurately predict vibrational entropies of L1₂-ordered and disordered phases in Cu₃Au, Au₃Pd, Pd₃Au, Cu₃Pd, and Pd₃Au. In addition, we calculate the vibrational entropy difference between L1₂-ordered and disordered phases of Au₃Cu and Cu₃Pt.