Effect of full potential treatment of semi-core states on shear elastic constants*

In ab initio electronic structure calculations, the core-states are usually treated as bound state and are calculated by solving the Kohn-Sham equation with spherical potential approximation and an appropriate boundary condition. While in most cases such treament of the core states works well, under certain circumtances, e.g. materials under high pressure or with strong mechanical anisotropy, the non-spherical crystal field has significant effects on the semi-core electronic states, and consequently on the physical and chemical properties of the materials. In this presentation, we show a full-potential Green function approach to the treatment of the semi-core states which does not require the spherical potential approximation. We discuss the effect of semi-core states on the equation of state and elastic constants for bcc, fcc and hcp bulk metallic materials. Our calculations show that the full potential treatment of semi-core states causes the equilibrium lattice constant to decrease and the bulk moduli to increase. We find that the full-potential treatments improve the elastic constants c_ij, especially shear elastic constant c₄₄ results.