Charge and Spin Selfconsistent Kkr-Cpa Methodology for Complex Multi-Component Alloys
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CHARGE AND SPIN SELFCONSISTENT KKR-CPA METHODOLOGY FOR COMPLEX MULTI-COMPONENT ALLOYS A. Bansil 1 , S. Kaprzyk 1'2 , and J. Tobola 2 1 2Department of Physics, Northeastern University, Boston, MA 02115 Institute of Physics and Nuclear Techniques, Academy of Mining and Metallurgy, Al. Mickiewicza 30, Cracow 30059, Poland ABSTRACT We have developed the charge and spin selfconsistent KKR-CPA approach for a first-principles parameter free treatment of disorder effects in complex multi-component alloys. The nature of the KKR-CPA Green's function in the complex energy plane is discussed. A generalized Lloyd formula for the density of states is obtained and some subtle features of the formalism are pointed out. We illustrate our KKR-CPA methodology by giving a number of examples of magnetic as well as non-magnetic systems. The non-magnetic cases considered are the simple cubic perovskites Ba.K 1_0 BiO3 and BaPb..-Bi,0 3 , and the high-Te superconductor La 2 -. Sr.CuO4 for the body-centeredtetragonal phase. The examples of magnetic systems discussed are, the the Heusler alloys Co 2 _.Fe0 MnSi (L2 1 structure), and the semi-magnetic semiconductor Cdl_.Mn.Te in the zincblende structure.
I. INTRODUCTION The electronic structure and properties of complex materials have drawn an increasing interest in recent years, spurred in part by the discovery of the high-T, superconductors which mostly involve complex phases. While reliable predictions of the electronic structures of ordered compounds with many atoms per unit cell have been obtained using the local density approximation, a comparable description of the disordered phases has been lagging, even though wide variations in properties with different substitutions are commonly observed. The band theory of ordered phases is not suited for exploring a variety of phenomena in materials, and it is clear that the first-principles KKR-CPA approach, which has already proven successful in simple binary alloys[1-5], needs to be generalized to treat complex systems. It should be noted however that limited progress can often be made via the use of virtual crystal, rigid band, and supercell-type models and also via the tight-binding CPA framework with parameters chosen to fit the band structures of the end-compounds.J6] Nevertheless, as the extensive experience with binary alloys shows, the simpler tight-binding CPA and rigid band type models cannot be expected to provide a realistic description of the disordered phases; if anything, these simpler models are likely to become generally less reliable as the complexity of the unit cell increases. With this motivation, we have developed and implemented the charge and spin selfconsistent KKR-CPA approach to treat disorder effects in complex materials on a first-principles basis. No free parameters other than the lattice data are involved; this restriction may also be removed, at least in principle, by minimizing the total energy of the system as a function of the interatomic spacings. Concerning our formulation of the multi-component KKR-CPA meth
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