Many-body anharmonic interactions in Ag and Ni

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Abstract
A many-body force approach is adopted to calculate the thermoelastic properties of Ag and Ni. The method of homogeneous deformation permits the anharmonic potential parameters to be related to the experimentally known thirdorder elastic constants. Both second- and third-order Cauchy relations are violated by this many-body potential. We have used a strain-dependent perturbative Helmholtz free energy to evaluate the linear thermal expansion coefficient and the thermodynamic Gruneisen parameter of both metals. Good agreement between theory and experiment is found. Our results suggest that, to fit thermodynamical properties, many-body interactions have to be included in the anharmonic part of the potential.