Development of n-body potentials for hcp-bcc and fcc-bcc binary transition metal systems

Within the framework of the second-moment approximation of the tight-binding theory, n-body potentials are proposed for hcp, fcc and bcc transition metals and their alloys. Both the energies and their derivatives calculated from the proposed potentials go smoothly to zero at cutoff radii, thus avoiding the unphysical behaviors that may emerge in simulations. With the assistances of ab initio calculations, the proposed potentials are then applied to Zr, Hf, Cu, V, Nb, Ta and their binary alloys. It turns out that the n-body potentials can well predict the energy sequence of stable and metastable structures of these metals. The vacancy formation energies, surface energies and melting points derived from the potentials also match well with experimental results. Based on the constructed potentials, molecular dynamics simulations reveal that Cu-Nb and Zr-Nb metallic glasses could be formed within the composition range of about 15-72 and 8-80 at.% Nb, respectively, matching well with experimental observations. Voronoi analyses reveal that the dominating atomic packings in Cu-Nb metallic glasses are the icositetrahedron (CN = 14), icosihexahedron (CN = 15) and icosidihedron (CN = 13) with fractions of 33%, 26% and 21%, respectively.