Computation of the Peierls stress in tantalum with an extended-range modified embedded atom method potential

When computing the Peierls stress of screw dislocations in tantalum by means of classical molecular dynamics (CMD), we have observed that a suitable potential should be able to reproduce the complicated angular dependence of forces arising in the core structure of dislocations. This prevents the use of simple embedded atom potentials, but we notice that more generally, effective interatomic potentials tend to overestimate the Peierls stress. Since the Peierls-Nabarro model of dislocation requires an accurate description of the generalized stacking fault (GSF) energy surface, we have decided to use the modified embedded atom method (MEAM) potential, which explicitly incorporates angular terms, whose coefficients are constrained to reproduce ab initio GSF data. Calculations with our new tantalum empirical model show the importance of hard core screw dislocations and underline the problem of kinetics in Peierls stress calculations.