Analytic modified embedded atom potentials for HCP metals

Abstract

Analytic modified embedded atom method (AMEAM) type many-body potentialshave been constructed for ten hcp metals: Be, Co, Hf, Mg, Re, Ru, Sc, Ti, Yand Zr. The potentials are parametrized using analytic functions and fittedto the cohesive energy, unrelaxed vacancy formation energy, fiveindependent second-order elastic constants and two equilibrium conditions.Hence, each of the constructed potentials represents a stable hexagonalclose-packed lattice with a particular non-ideal c/a ratio. In order totreat the metals with negative Cauchy pressure, a modified term has beenadded to the total energy. For all the metals considered, the hcp latticeis shown to be energetically most stable when compared with the fcc and bccstructure and the hcp lattice with ideal c/a. The activation energy forvacancy diffusion in these metals has been calculated. They agree well withexperimental data available and those calculated by other authors for bothmonovacancy and divacancy mechanisms and the most possible diffusion pathsare predicted. Stacking fault and surface energy have also been calculatedand their values are lower than typical experimental data. Finally, theself-interstitial atom (SIA) formation energy and volume have beenevaluated for eight possible sites. This calculation suggests that thebasal split or crowdion is the most stable configuration for metals with arather large deviation from the ideal c/a value and the non-basaldumbbell (C or S) is the most stable configuration for metals with c/anear ideal. The relationship between SIA formation energy and meltingtemperature roughly obeys a linear relation for most metals except Ru andRe.