Coherent potential approximation

About: Coherent potential approximation is a research topic. Over the lifetime, 1930 publications have been published within this topic receiving 36805 citations.

Hydrogen Adsorption on Ordered and Disordered Pt-Ni Alloys

Abstract: The bulk properties and chemical reactivity of disordered Pt-Ni alloys in the A1 (fcc) structure are investigated using different methods: Virtual Crystal Approximation (VCA), Korringa–Kohn–Rostoker Coherent Potential Approximation (KKR-CPA), and large explicit supercells generated using Super-Cell Random Approximates (SCRAPs). While VCA predicts lattice constants that closely follow Vegard’s law, the large supercells and KKR-CPA predict lattice constants that are consistently larger than Vegard’s law. KKR-CPA results closely agree with those from the large supercells for the disordered alloys, producing similar projected density of states and magnetic moment across the composition range. For instance, while VCA predicts the disordered alloys to be non-magnetic at a Pt concentration (xPt) ≥ 0.5, KKR-CPA and SCRAPs predict the disordered alloys to remain ferromagnetic to higher Pt concentrations. As xPt decreases, the adsorption of H becomes more exothermic on bulk-terminated (111) surfaces but less exothermic on Pt monolayer-terminated (111) surfaces due largely to strain effects. (111) surfaces cut from the large supercells predict average H adsorption energies on the disordered alloys similar to those on the ordered phases of the same compositions, while VCA predicts H adsorption to be more exothermic.

Multi-band coherent potential approximation applied to ferromagnetic nickel-ruthenium alloys

Abstract: In the present multi-band CPA calculation, the spin-dependent potential is treated in the Hartree-Fock (HF) approximation. The host (Ni) parameters are chosen self-consistently. Various solutions are discussed depending upon the choice of the Ru parameters and the solution which is consistent with the experimental situation and also satisfies energy considerations is accepted. Its salient features are fairly sharp impurity virtual bound states around EF for low Ru concentration. The variation of the site moment, and the Ru concentration at which the transition to the paramagnetic state occurs, are in accord with magnetisation data. However, the predicted variation of the site moment asphericity with Ru concentration for very low Ru disagrees with polarised neutron data. A possible reason for this discrepancy is discussed. Finally, the authors conclude that the CPA, like any other mean field theory, is able to predict broadly the observed features in an NiRu system which is characterised by strong local environmental effects.

Antiferromagnetic instability of heavy-fermion alloys with conduction band impurities

Abstract: The antiferromagnetic instability of heavy-fermion alloys with conduction band impurities is examined in the single-site coherent-potential approximation with the strong correlation treated by the slave-boson technique of Kotliar and Ruckenstein. The variation of the paramagnetic-antiferromagnetic phase boundary with the impurity concentration is studied in the case of isoelectronic doping. Our results show that the isoelectronic doping favours the formation of antiferromagnetism if the impurities increase the cell volume, thus suppressing the c-f mixing, which is in agreement with experimental observations in Ce(Cu1-xAgx)6 and Ce(Cu1-xAux)6. The obtained phase diagram can also be used to explain the effect of nonisoelectronic substitutions of Al for Cu in CeCu6.

Chapter 10 Computational Nano‐Materials Design for the Wide Band‐Gap and High‐TC Semiconductor Spintronics

Abstract: Publisher Summary This chapter presents a unified physical picture of wide band-gap II–VI and III–V DMS—such as ZnO, ZnS, ZnSe, ZnTe, and GaN—on the basis of the state-of-the-art ab initio electronic structure calculation done by using the Korringa–Kohn–Rostoker coherent potential approximation and local density approximation (KKR–CPA–LDA) and the self-interaction corrected LDA (SIC-LDA) to go beyond the LDA. Zener's double-exchange interaction and superexchange interaction mechanisms are dominant in the magnetic magnetism. In the homogeneous system, the calculated Curie temperature (TC) obtained by using a Monte Carlo simulation (MCS) and electronic structure is in good agreement with the experiment (TC and photoemission spectroscopy [PES]). In the inhomogeneous system, the chapter presents a 3D Dairiseki phase and a 1D Konbu phase caused by spinodal nano-decomposition. A design of a growth position and shape-control method for nanomagnets in the superstructure by using self-organization is discussed. Finally, on the basis of the ferromagnetic (FM) mechanism of Zener's double-exchange mechanism, the chapter discusses a design of a new class of half-metallic ferromagnets without 3d transition metal (TM) impurities, such as C- or N-doped CaO, BaO, MgO, SrO, and SiO2.