Vibrational properties of vacancy in bcc Nb using embedded atom method

Abstract

Embedded atom method (EAM) with universal form of embedding function along with Morse form of pair potential have been employed to determine the potential for Nb by fitting to Cauchy pressure, shear constants, cohesive energy and vacancy formation energy. Obtained potential is used to calculate the phonon dispersion spectra of this metal. On comparing with experimental phonons, the results using EAM show large discrepancies. In order to overcome this inadequacy of EAM model, we have further employed a modified embedded atom method (MEAM) in which a modified term along with pair potential and embedding function are added in the total energy. Calculated phonon dispersions using the potential obtained from MEAM are found to be closer to experimental results compared to those obtained from EAM. With application of MEAM potential, we have computed local vibrational density of states of atoms in ideal lattice and neighbouring atoms for vacancy. Vacancy formation entropy and mean square thermal displacements of the neighbouring atoms of vacancy are obtained using Green’s function method.