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 ( Δ 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 Δ 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 α -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. [ABSTRACT FROM AUTHOR]