INSTITUTE OF PHYSICS PUBLISHING MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING Modelling Simul. Mater. Sci. Eng. 12 (2004) S371–S389 PII: S0965-0393(04)74281-3 Calculating the Peierls energy and Peierls stress from atomistic simulations of screw dislocation dynamics: application to bcc tantalum Guofeng Wang 1 , Alejandro Strachan 2 , Tahir ¸ Ca ˘ gın and William A Goddard III 3 Materials and Process Simulation Center, Beckman Institute (139-74), California Institute of Technology, Pasadena, CA 91125, USA E-mail: wag@wag.caltech.edu Received 17 September 2003 Published 10 June 2004 Online at stacks.iop.org/MSMSE/12/S371 doi:10.1088/0965-0393/12/4/S06 Abstract We introduce a novel approach to calculating the Peierls energy barrier (and Peierls stress) based on the analysis of the dislocation migration dynamics, which we apply to 1/2a〈111〉 screw dislocations in bcc Ta. To study the migration of screw dislocations we use molecular dynamics with a first principles based embedded-atom method force field for Ta. We first distinguish the atoms belonging to the dislocation core based on their atomic strain energies, defining the dislocation core as the 12 atoms with higher strain energies per Burgers vector. We then apply this definition to the moving dislocations (following the dynamics of a [1−10] dipole of 1/2〈111〉 screw dislocations at 0.001 K) and extract their Peierls energy barrier (E P ) and Peierls stress (τ P ). From the dynamics of a dislocation dipole, we determine E P = 0.032 eV (and τ P = 790 MPa) for twinning shear and E P = 0.068 eV (and τ P = 1430 MPa) for anti-twinning shear, in good agreement with the results by applying direct shear stresses. This dislocation dynamics method provides insights regarding the dislocation migration process, allowing us to determine the continuous path of dislocation migration. We find that under twinning shear the screw dislocation moves along a path at an angle of only 8.5˚ with the [1−10] direction while for anti-twinning shear it moves along a path at an angle of 29.5˚ with the [1−10] direction, documenting the magnitude of the violation of the Schmid Law. 1 Current address: Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA. 2 Current address: Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA. 3 Author to whom any correspondence should be addressed. 0965-0393/04/040371+19$30.00 © 2004 IOP Publishing Ltd Printed in the UK S371