Ab initioand finite-temperature molecular dynamics studies of lattice resistance in tantalum

We explore the apparent discrepancy between experimental data and theoretical calculations of the lattice resistance of bcc tantalum. We present an empirical potential calculation for the temperature dependence of the Peierls stress in this system and an ab initio calculation of the zero-temperature Peierls stress, which employs periodic boundary conditions, those best suited to the study of metallic systems at the electronic-structure level. Our ab initio value for the Peierls stress is over five times larger than current extrapolations of experimental lattice resistance to zero temperature. Although we find that the common techniques for such extrapolation indeed tend to underestimate the zero-temperature limit, the amount of the underestimation we observe is only 10%-20%, leaving open the possibility that mechanisms other than the lattice resistance to motion of an isolated, straight dislocation are important in controlling the process of low-temperature slip.