CALCULATION OF ELECTRONIC AND MAGNETIC-PROPERTIES OF TRANSITION-METALSURFACES - COMPARISON OF LMTO AND TIGHT-BINDING METHODS

Low-dimensional systems have attracted a great deal of attention durin g the past decade. The lowered symmetry and coordination number give r ise to new and interesting electronic and magnetic phenomena. Several ab initio numerical methods have been developed to calculate the elect ronic and magnetic structure of materials, but these calculations requ ire a great deal of computational effort. In order to study complex sy stems it is of interest to be able to make use of simpler approximativ e methods. For transition metals such an alternative approach is provi ded by the tight-binding approximation. Within the conventional parame trized tight-binding approach the lowered dimensionality of surfaces g ives rise to an unphysical filling of the surface d orbitals (spd char ge transfer), which in turn gives rise to lowered surface magnetizatio ns. Results obtained by applying the linear muffin-tin orbital (LMTO) method to a repeated sequence of slabs and empty spheres show the exis tence of a spillover coming from the s and essentially p surface orbit als, with the d-band occupation remaining nearly the same as in the bu lk materials. We suggest in this work a simple way of parametrizing th e tight-binding Hamiltonian in such a way that the characteristics obs erved in LMTO calculations are preserved and the simplicity of a tight -binding approach remains valid. This is obtained by only adding a new layer of orbitals on the surface in order to simulate the spillover. We compare in this contribution results for Rh, Fe, and Cu (001) monol ayers and five-layer slabs obtained using LMTO and an unrestricted Hub bard Hartree-Fock Hamiltonian with the surface parametrization.