Calculation of muffin-tin potentials and phase shifts. The role of the inner potential V0 EDAC

The muffin-tin potential is calculating by averaging the atomic potentials of the atoms contained in the cluster within muffin-tin spheres. Those atomic potentials are calculated using Desclaux's relativistic code (Comp. Phys. Comm. 9, 31 (1975)). For a given atomic number, the volume of the corresponding muffin-tin sphere is proportional to that of an sphere containing up to 80% of the 10 outer-most electrons of the isolated atom. The muffin-tin spheres are then scaled in such a way that they are touching. Atoms with identical atomic number can still have different muffin-tin potentials depending on their local environment. To avoid artificial effects introduced by the cluster termination, a sufficient number of extra atoms, besides those used in the multiple-scattering calculation, are introduced when a layer or a surface are specified.

The values of each muffin-tin potential are referred to the vacuum. However, a muffin-tin zero different from the vacuum level can be introduced in the interstitial region. This is taken as the inner potential V0, which is an input parameter in the EDAC front page. An automatic calculation of V0 would depend much on the choice of the cluster shape, so that this parameter is left to the user discretion.

Phase shifts are calculated for each different muffin-tin potential whenever the multiple scattering calculation is carried out. The relativistic code of Salvat and Mayol (Comp. Phys. Comm. 62, 65 (1991)) has been used for that purpose.