M. Lüders

Ab-initio theory of superconductivity - I: Density functional formalism and approximate functionals

An approach to the description of superconductors in thermal equilibrium is developed within a formally exact density functional framework. The theory is formulated in terms of three “densities:” the ordinary electron density, the superconducting order parameter, and the diagonal of the nuclear N-body density matrix. The electron density and the order parameter are determined by Kohn-Sham equations that resemble the Bogoliubov–de Gennes equations. The nuclear density matrix follows from a Schrodinger equation with an effective N-body interaction. These equations are coupled to each other via exchange-correlation potentials which are universal functionals of the three densities. Approximations of these exchange-correlation functionals are derived using the diagrammatic techniques of many-body perturbation theory. The bare Coulomb repulsion between the electrons and the electron-phonon interaction enter this perturbative treatment on the same footing. In this way, a truly ab initio description is achieved which does not contain any empirical parameters.

Ab initio theory of superconductivity. II. Application to elemental metals

The density functional theory for superconductors developed in the preceding article is applied to the calculation of superconducting properties of several elemental metals. In particular, we present results for the transition temperature, for the gap at zero temperature, and for thermodynamic properties like the specific heat. We obtain an unprecedented agreement with experimental results. Superconductors with both strong and weak electron-phonon coupling are equally well described. This demonstrates that, as far as conventional superconductivity is concerned, the first-principles prediction of superconducting properties is feasible.

Structural phase transitions and fundamental band gaps of MgxZn1-xO alloys from first principles

Received 29 April 2009; revised manuscript received 27 June 2009; published 6 October 2009 The structural phase transitions and the fundamental band gaps of MgxZn1�xO alloys are investigated by detailed first-principles calculations in the entire range of Mg concentrations x, applying a multiple-scattering theoretical approach Korringa-Kohn-Rostoker method. Disordered alloys are treated within the coherentpotential approximation. The calculations for various crystal phases have given rise to a phase diagram in good agreement with experiments and other theoretical approaches. The phase transition from the wurtzite to the rock-salt structure is predicted at the Mg concentration of x = 0.33, which is close to the experimental value of 0.33–0.40. The size of the fundamental band gap, typically underestimated by the local-density approximation, is considerably improved by the self-interaction correction. The increase in the gap upon alloying ZnO with Mg corroborates experimental trends. Our findings are relevant for applications in optical, electrical, and, in particular, in magnetoelectric devices.

Superconducting Properties ofMgB2from First Principles

Solid MgB(2) has rather interesting and technologically important properties, such as a very high superconducting transition temperature. Focusing on this compound, we report the first nontrivial application of a novel density-functional-type theory for superconductors, recently proposed by the authors. Without invoking any adjustable parameters, we obtain the transition temperature, the gaps, and the specific heat of MgB(2) in very good agreement with experiment. Moreover, our calculations show how the Coulomb interaction acts differently on sigma and pi states, thereby stabilizing the observed superconducting phase.

Exchange coupling in transition metal monoxides: Electronic structure calculations

An ab initio study of magnetic-exchange interactions in antiferromagnetic and strongly correlated 3d transition metal monoxides is presented. Their electronic structure is calculated using the local self-interaction correction approach, implemented within the Korringa-Kohn-Rostoker band-structure method, which is based on multiple scattering theory. The Heisenberg exchange constants are evaluated with the magnetic force theorem. Based on these the corresponding Neel temperatures TN and spin-wave dispersions are calculated. The Neel temperatures are obtained using mean-field approximation, random-phase approximation and Monte Carlo simulations. The pressure dependence of TN is investigated using exchange constants calculated for different lattice constants. All the calculated results are compared to experimental data.

Self-interaction correction in multiple scattering theory

We propose a simplified version of self-interaction corrected local spin-density (SIC-LSD) approximation, based on multiple scattering theory, which implements self-interaction correction locally, within the KKR method. The multiple scattering aspect of this new SIC-LSD method allows for the description of crystal potentials which vary from site to site in a random fashion and the calculation of physical quantities averaged over ensembles of such potentials using the coherent potential approximation (CPA). This facilitates applications of the SIC to alloys and pseudoalloys which could describe disordered local moment systems, as well as intermediate valences. As a demonstration of the method, we study the well-known

Ab initio angle-resolved photoemission in multiple-scattering formulation

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Towards efficient data exchange and sharing for big-data driven materials science: metadata and data formats

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Rare-earth pnictides and chalcogenides from first-principles

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Chapter 241 The Dual, Localized or Band‐Like, Character of the 4f‐States

phase transition in Ce, where we also explain how SIC operates in terms of multiple scattering theory.