Berlin 2012 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 35: Topical Session Theory meets Experiment III - Bond-order Potentials and Finite Temperature
MM 35.3: Vortrag
Mittwoch, 28. März 2012, 15:45–16:00, TC 006
Bond-order potentials for bcc transition metals — •Miroslav Cak, Thomas Hammerschmidt, and Ralf Drautz — ICAMS, Ruhr-Universität Bochum, Bochum, Germany
Bond-order potentials (BOPs) are based on the tight-binding approximation for determining the energy of a system of many interacting atoms. We present newly developed parametrisations of analytic BOPs for the refractory metals Tungsten, Molybdenum, Niobium and Tantalum. These metals play an important role as strengtheners of nickel-based superalloys and in topologically close-packed (TCP) phase precipitates in steels. Theory parameters of the analytic BOPs were optimised for the equilibrium bcc structure and extensively tested for atomic environments far from equilibrium that have not been included in the fitting procedure. These tests include structural energy differences for different competing structures; tetragonal, trigonal, hexagonal and orthorhombic deformation paths; formation energies of point defects and phonon dispersion relations. Comparing our calculations to corresponding first-principles, tight-binding and experimental results shows a very good transferability of our analytic BOPs to atomic structures encountered in lattice defects. From phonon densities of states we calculated heat capacities CV at room temperatures that are in good agreement with experimental values. The new analytic BOPs were also applied to the calculation of melting temperatures using molecular dynamics simulations. Our results are in reasonable agreement with experiment and confirm that our BOPs capture the refractory character of W, Mo, Nb and Ta.