A first-principles theory of the strain-effect electric field gradient in cubic metals due to point defects

A theory has been developed to evaluate on a first-principles basis the electric field gradient tensors due to the lattice strain produced by the introduction of point defects in cubic host metals. The lattice for this purpose has been divided into two regions, namely a near region and a far region. The former surrounds the defect site and extends over several near-neighbour cells and the latter represents the remaining part of the lattice. The contribution to the electric field gradient from the ions in the near region has been evaluated to all orders of lattice strain by using the realistic lattice displacements obtained for a discrete lattice in lattice statics calculations. The contribution from the far region, on the other hand, has been calculated in the continuum model of the lattice by retaining the effect of strain to first order only. Unlike in other calculations, no adjustable parameter has been used. The contribution from the valence effect has been evaluated by using the screening charge distribution from scattering theory. The results for the net electric field gradients in Cu and Al hosts due to monovacancies show significant improvement over those obtained by using the continuum model lattice strain for the whole region.