STRESS TENSOR IN REAL-SPACE KOHN-SHAM DENSITY FUNCTIONAL THEORY

An accurate and efficient formulation of the stress tensor for real-space Kohn-ShamDensity Functional Theory (DFT) calculations is presented. Specifically, while employinga local formulation of the electrostatics, a linear-scaling expression for the stress tensorthat is applicable to simulations with unit cells of arbitrary symmetry, semilocal exchange-correlation functionals, and Brillouin zone integration is discussed. In particular, the contri-butions arising from the self energy and the nonlocal pseudopotential energy are rewrittento make them suitable for the real-space finite-difference discretization, achieving up tothree orders of magnitude improvement in the accuracy of the computed stresses. Throughselected examples representative of static calculations, the accuracy and efficiency of theproposed formulation is verified. In particular, high rates of convergence with spatial dis-cretization, consistency between the computed energy and stress tensor, and very goodagreement with reference planewave results are demonstrated.M.S