Angular momentum convergence of Korringa-Kohn-Rostoker Green's function methods

The convergence of multiple-scattering-theory-based electronic structure methods (e.g. the Korringa-Kohn-Rostoker (KKR) band theory method), is determined by l(max), the maximum value of the angular momentum quantum number l. It has been generally assumed that l(max) = 3 or 4 is sufficient to ensure a converged ground state and other properties. Using the locally self-consistent multiple-scattering method, which facilitates the use of very high values of l(max), it is shown that the convergence of KKR Green's function methods is much slower than previously supposed, even when spherical approximations to the crystal potential are used. Calculations for Cu using 3 less than or equal to l(max) less than or equal to 16 indicate that the total energy is converged to within similar to0.04 mRyd l(max) = 12. For both face-centred cubic and body-centred cubic structures, the largest error in the total energy occurs at l(max) = 4; l(max) = 8 gives total energies, bulk moduli, and lattice constants that are converged to accuracies of 0.1 mRyd, 0.1 Mbar, and 0.002 Bohr respectively.