Choice of the muffin tin zero in Fermi surface interpolation schemes based on phase shifts

Abstract

It appears, that the diagonal and the important off-diagonal APW matrix elements in the ‘on the Fermi sphere’ approximation are approximately conserved for different values of the Fermi energy parameter E F in an APW interpolation scheme for the Fermi surface of white tin. The same applies for the matrix elements in a KKRZ interpolation scheme for the Fermi surfaces of Cu and Ag. From this empirical conservation law one can understand the functional behaviour of the logarithmic derivative of the l-th radial wave function and of the Friedel sum Z F as a function of E F·Z F is then approximately zero for E F = E 0 F (nearly free electron value) and approximately Z (the valence) for E F = E 0 F 3 . One can get some feeling for the role of E F in APW and KKRZ interpolation schemes by focussing on a comparison with local pseudopotential form factors.