Arithmetic extraction of elastic constants of cubic crystals from first-principles calculations of stress

In the extraction of elastic constants of cubic crystals from first-principles calculations of energy or stress, the relative deviation of the adopted lattice-constants from true values (Delta a/a(0)) is inevitably added to the diagonal components of the applied elastic strains, which might lead to sizeable inaccuracy of bulk modulus B and tetragonal shear modulus C'. This paper suggests an arithmetic scheme that dramatically decrease the error transfer from Delta a/a(0) in the extraction of B and C' from first-principles calculations of stress. By using this scheme, we compute the elastic constants of alpha-Fe, which are all in good agreement with those extracted by least-squares scheme from the same level first-principles calculations of energy and stress. The computed Young's modulus E and polycrystalline shear modulus G of Fe-base binary alloys at alloy concentration of 0.78 at.% are both satisfactorily consistent with the data at 0 K deduced from the available experimental measurements. Theoretical basis and tests both indicate that the suggested scheme is accurate and efficient in extracting elastic constants of cubic crystals at equilibrium. (C) 2014 Elsevier B. V. All rights reserved.