A full-potential approach to the solution of core states

For an ab intio, all-electron, electronic structure calculation method, e.g. KKR, LMTO, calculating the core states associated with each atom in unit cell is a necessary procedure during its self-consistent iterations. In this procedure, the energy eigenvalue and the electron density of the core states are obtained by solving the Kohn-Sham equation, with boundary conditions that the wavefunction solutions become zero beyond a certain distance from the nucleus, e.g., the muffin-tin radius. Despite that a full-potential method is required for solving the valence states when muffin-tin potential approximation becomes invalid, the core states are still solved with the potential in muffin-tin form. In this presentation, we show a full-potential method, based on scattering theory, for calculating the core states. In this approach, we developed a fast method for searching the poles of S-matrix to find the core state energy eigenvalues, and we applied a Green function technique to calculate the electron density associated with the core states. As a result, the solutions for both valence and core states correspond to the same one-electron potential. This method enables proper treatment of shallow core states, which appear in materials under high pressure with high lattice distortions.