It was recalled that the bond-order potential for transition metals was a real-space semi-empirical description of interactions, between atoms, which was based upon the tight-binding approximation and the d-band model. This scheme provided a direct bridge between electronic level modeling and atomistic modeling, where the electronic degrees of freedom were coarse-grained into many-body interatomic potentials. A bond-order potential was constructed here in which both the attractive and repulsive contributions to the binding energy were environmentally dependent, due to a non-orthogonality of the orbitals and a breathing of the screening charges. Firstly, the energies of alternative crystal structures (A15, face-centered cubic, hexagonal close-packed, simple cubic) were calculated and compared with those evaluated ab initio. The transferability of the bond-order potential to atomic configurations that deviated significantly from the body-centered cubic lattice was studied by calculating the energies for tetragonal, trigonal and hexagonal transformation paths. The phonon spectra were then evaluated for various symmetrical crystallographic directions and were compared with available experiments. The calculations highlighted the importance of directional bonding, and an investigation of phonons demonstrated that the environmental dependence of the bond integrals was essential if the phonons of the N branch were not to be unphysically soft. Finally, the constructed bond-order potential was used to model the core structure and glide of ½<111> screw dislocations. The predicted structure of the core agreed well with that found from ab initio calculations, and the observed glide behavior not only agreed with available ab initio data but was also in agreement with many experimental observations. It explained the main reason for the breakdown of the Schmid law in body-centered cubic metals.

Bond-Order Potential for Molybdenum - Application to Dislocation Behavior. M.Mrovec, D.Nguyen-Manh, D.G.Pettifor, V.Vitek: Physical Review B, 2004, 69[9], 094115 (16pp)