Screened KKR with hard-core potentials

We developed a self-consistent screened-Korringa± Kohn± Rostoker (KKR) method in an ab initio tight-binding formulation. The reduction in numerical e€ ort in comparison with that required for the standard KKR method is achieved by the choice of a suitable reference system. Following the idea of Zeller et al. (1995, Phys. Rev. B, 52, 8807), reference systems with repulsive mu n-tin potentials of constant height are considered. This paper is dedicated to reference potentials of in® nite height, so-called hard core potentials. It will be demonstrated that the advantage of the analytical solution to the scattering problem is accompanied by a reduced accuracy of the screened KKR method for close-packed hard spheres. To overcome this problem, we consider hard spheres with a reduced diameter. The best results also in comparison with reference potentials of ® nite height are obtained using hard spheres with a radius reduced to about 80% of the mu n-tin value. The past decades have been characterized by new experimental techniques that allow the production and preparation of nanostructural metallic systems, for example ® lms, multilayers and nanowires. These materials exhibit new physical properties such as interlayer exchange coupling (IEC) and giant magnetoresistance (GMR), which are extremely interesting for potential applications in magnetoelectronics. Consequently, a large variety of experimental and theoretical investigations was initiated to elucidate the microscopic origin of the phenomena. For this reason, there is a strong need for reliable ab initio calculations of electronic structure. Because of the complexity of the systems considered, new ab initio methods have to be developed. The numerical e€ ort required by standard electronic structure schemes increases with the third power of the number N of atoms in the unit cell. The newly developed ab initio tight-binding methods, however, scale linearly with N and maintain the high accuracy of the standard methods. Using the Korringa± Kohn± Rostoker (KKR) scheme the electronic structure is described by a Green function (GF). Within the multiple-scattering theory, the GF can be separated in a single site and a structura l contribution. The structura l Green functions of two di€ erent systems with VÊ (r) and V (r) are connected by an algebraic Dyson equation: G L L  (E ) = G Ê Â L L  (E ) + n   ,L   G Ê Â Â L L   (E ) (t t )   l   (E )G   L   L  (E ) ; (1) 0141± 8637/98 $12.00 Ñ 1998 Taylor & Francis Ltd. with the single site t-matrices for spherical scatterers