First principles force field for metallic tantalum

We develop a many-body force field (FF) for tantalum based on extensive ab initio quantum mechanical (QM) calculations and illustrate its application with molecular dynamics (MD). As input data to the FF we use ab initio methods (LAPW-GGA) to calculate: (i) the zero temperature equation of state (EOS) of Ta for bcc, fcc, and hcp crystal structures for pressures up to ∼500 GPa, and (ii) elastic constants. We use a mixed-basis pseudopotential code to calculate: (iii) volume-relaxed vacancy formation energy also as a function of pressure. In developing the Ta FF we also use previous QM calculations of: (iv) the EOS for the A15 structure; (v) the surface energy bcc (100); (vi) energetics for shear twinning of the bcc crystal. We find that, with appropriate parameters, an embedded atom model FF (denoted as qEAM FF) is able to reproduce all this QM data. We illustrate the use of the qEAM FF with MD to calculate such finite temperature properties as the melting curve up to 300 GPa and thermal expansivity in a wide temperature range. Both our predictions agree well with experimental values.