Green function for crystal surfaces I Original Research Article

The described computer code allows to calculate the surface Green function (SGF) of a semi-infinite solid with two-dimensional translational symmetry, using the layer Korringa-Kohn-Rostoker (KKR) approach within the muffin-tin approximation. The crystal is composed from planar or rumpled atomic layers, i.e., the atomic positions within the layer unit cell at the surface may differ from their ideal (bulk) values. The system may be divided into four regions of commensurable, two-dimensional lattice vectors, but with possibly different muffin-tin zeros and geometries: (i) vacuum region, (ii) overlayer, (iii) surface or subsurface region, (iv) substrate (bulk) region. The unit cell of any layer may be composed of any required number of different atoms. The Green function is evaluated in a spherical-wave expansion up to any maximum quantum number of angular momentum, with basis functions centered at the atomic sites. The following quantities can be computed from the SGF: (i) the electronic charge density, both for given energy E and Bloch vector k⊥ and totally, i.e., integrated over E and k⊥, and (ii) the local density of states (LDOS), either for a given k⊥ and projected onto a given angular momentum, L ≡ (l, m), (partial LDOS) or totally, i.e., integrated over k⊥ and summed up over L.