@article{18557, abstract = {{We describe the software package SPEX, which allows first-principles calculations of quasiparticle and collective electronic excitations in solids using techniques from many-body perturbation theory. The implementation is based on the full-potential linearized augmented-plane-wave (FLAPW) method, which treats core and valence electrons on an equal footing and can be applied to a wide range of materials, including transition metals and rare earths. After a discussion of essential features that contribute to the high numerical efficiency of the code, we present illustrative results for quasiparticle band structures calculated within the GW approximation for the electronic self-energy, electron-energy-loss spectra with inter- and intraband transitions as well as local-field effects, and spin-wave spectra of itinerant ferromagnets. In all cases the inclusion of many-body correlation terms leads to very good quantitative agreement with experimental spectroscopies.}}, author = {{Schindlmayr, Arno and Friedrich, Christoph and Şaşıoğlu, Ersoy and Blügel, Stefan}}, issn = {{2196-7156}}, journal = {{Zeitschrift für Physikalische Chemie}}, number = {{3-4}}, pages = {{357--368}}, publisher = {{Oldenbourg}}, title = {{{First-principles calculation of electronic excitations in solids with SPEX}}}, doi = {{10.1524/zpch.2010.6110}}, volume = {{224}}, year = {{2010}}, } @article{18632, abstract = {{We present measurements of the effective electron mass in biaxial tensile strained silicon on insulator (SSOI) material with 1.2 GPa stress and in unstrained SOI. Hall-bar metal oxide semiconductor field effect transistors on 60 nm SSOI and SOI were fabricated and Shubnikov–de Haas oscillations in the temperature range of T=0.4–4 K for magnetic fields of B=0–10 T were measured. The effective electron mass in SSOI and SOI samples was determined as mt=(0.20±0.01)m0. This result is in excellent agreement with first-principles calculations of the effective electron mass in the presence of strain.}}, author = {{Feste, Sebastian F. and Schäpers, Thomas and Buca, Dan and Zhao, Qing Tai and Knoch, Joachim and Bouhassoune, Mohammed and Schindlmayr, Arno and Mantl, Siegfried}}, issn = {{1077-3118}}, journal = {{Applied Physics Letters}}, number = {{18}}, publisher = {{American Institute of Physics}}, title = {{{Measurement of effective electron mass in biaxial tensile strained silicon on insulator}}}, doi = {{10.1063/1.3254330}}, volume = {{95}}, year = {{2009}}, } @inproceedings{18634, abstract = {{A computational method to obtain optical conductivities from first principles is presented. It exploits a relation between the conductivity and the complex dielectric function, which is constructed from the full electronic band structure within the random-phase approximation. In contrast to the Drude model, no empirical parameters are used. As interband transitions as well as local-field effects are properly included, the calculated spectra are valid over a wide frequency range. As an illustration I present quantitative results for selected simple metals, noble metals, and ferromagnetic transition metals. The implementation is based on the full-potential linearized augmented-plane-wave method.}}, author = {{Schindlmayr, Arno}}, booktitle = {{Theoretical and Computational Nanophotonics: Proceedings of the 2nd International Workshop}}, editor = {{Chigrin, Dmitry N.}}, isbn = {{978-0-7354-0715-2}}, issn = {{1551-7616}}, location = {{Bad Honnef}}, number = {{1}}, pages = {{157--159}}, publisher = {{American Institute of Physics}}, title = {{{Optical conductivity of metals from first principles}}}, doi = {{10.1063/1.3253897}}, volume = {{1176}}, year = {{2009}}, } @article{18636, abstract = {{We derive formulas for the Coulomb matrix within the full-potential linearized augmented-plane-wave (FLAPW) method. The Coulomb matrix is a central ingredient in implementations of many-body perturbation theory, such as the Hartree–Fock and GW approximations for the electronic self-energy or the random-phase approximation for the dielectric function. It is represented in the mixed product basis, which combines numerical muffin-tin functions and interstitial plane waves constructed from products of FLAPW basis functions. The interstitial plane waves are here expanded with the Rayleigh formula. The resulting algorithm is very efficient in terms of both computational cost and accuracy and is superior to an implementation with the Fourier transform of the step function. In order to allow an analytic treatment of the divergence at k=0 in reciprocal space, we expand the Coulomb matrix analytically around this point without resorting to a projection onto plane waves. Without additional approximations, we then apply a basis transformation that diagonalizes the Coulomb matrix and confines the divergence to a single eigenvalue. At the same time, response matrices like the dielectric function separate into head, wings, and body with the same mathematical properties as in a plane-wave basis. As an illustration we apply the formulas to electron-energy-loss spectra (EELS) for nickel at different k vectors including k=0. The convergence of the spectra towards the result at k=0 is clearly seen. Our all-electron treatment also allows to include transitions from 3s and 3p core states in the EELS spectrum that give rise to a shallow peak at high energies and lead to good agreement with experiment.}}, author = {{Friedrich, Christoph and Schindlmayr, Arno and Blügel, Stefan}}, issn = {{0010-4655}}, journal = {{Computer Physics Communications}}, number = {{3}}, pages = {{347--359}}, publisher = {{Elsevier}}, title = {{{Efficient calculation of the Coulomb matrix and its expansion around k=0 within the FLAPW method}}}, doi = {{10.1016/j.cpc.2008.10.009}}, volume = {{180}}, year = {{2009}}, } @article{18564, abstract = {{In the context of photoelectron spectroscopy, the GW approach has developed into the method of choice for computing excitation spectra of weakly correlated bulk systems and their surfaces. To employ the established computational schemes that have been developed for three-dimensional crystals, two-dimensional systems are typically treated in the repeated-slab approach. In this work we critically examine this approach and identify three important aspects for which the treatment of long-range screening in two dimensions differs from the bulk: (1) anisotropy of the macroscopic screening, (2) k-point sampling parallel to the surface, (3) periodic repetition and slab-slab interaction. For prototypical semiconductor (silicon) and ionic (NaCl) thin films we quantify the individual contributions of points (1) to (3) and develop robust and efficient correction schemes derived from the classic theory of dielectric screening.}}, author = {{Freysoldt, Christoph and Eggert, Philipp and Rinke, Patrick and Schindlmayr, Arno and Scheffler, Matthias}}, issn = {{1550-235X}}, journal = {{Physical Review B}}, number = {{23}}, publisher = {{American Physical Society}}, title = {{{Screening in two dimensions: GW calculations for surfaces and thin films using the repeated-slab approach}}}, doi = {{10.1103/PhysRevB.77.235428}}, volume = {{77}}, year = {{2008}}, } @inbook{18588, author = {{Schindlmayr, Arno}}, booktitle = {{Probing the Nanoworld }}, editor = {{Urban, Knut and Schneider, Claus Michael and Brückel, Thomas and Blügel, Stefan}}, isbn = {{978-3-89336-462-6}}, issn = {{1433-5506}}, location = {{Jülich}}, pages = {{A1.21--A1.36}}, publisher = {{Forschungszentrum Jülich}}, title = {{{Interaction of radiation with matter. Part II: Light and electrons}}}, volume = {{34}}, year = {{2007}}, } @article{18589, abstract = {{For the calculation of neutral excitations, time-dependent density functional theory (TDDFT) is an exact reformulation of the many-body time-dependent Schrödinger equation, based on knowledge of the density instead of the many-body wavefunction. The density can be determined in an efficient scheme by solving one-particle non-interacting Schrödinger equations—the Kohn–Sham equations. The complication of the problem is hidden in the—unknown—time-dependent exchange and correlation potential that appears in the Kohn–Sham equations and for which it is essential to find good approximations. Many approximations have been suggested and tested for finite systems, where even the very simple adiabatic local-density approximation (ALDA) has often proved to be successful. In the case of solids, ALDA fails to reproduce optical absorption spectra, which are instead well described by solving the Bethe–Salpeter equation of many-body perturbation theory (MBPT). On the other hand, ALDA can lead to excellent results for loss functions (at vanishing and finite momentum transfer). In view of this and thanks to recent successful developments of improved linear-response kernels derived from MBPT, TDDFT is today considered a promising alternative to MBPT for the calculation of electronic spectra, even for solids. After reviewing the fundamentals of TDDFT within linear response, we discuss different approaches and a variety of applications to extended systems.}}, author = {{Botti, Silvana and Schindlmayr, Arno and Del Sole, Rodolfo and Reining, Lucia}}, issn = {{1361-6633}}, journal = {{Reports on Progress in Physics}}, number = {{3}}, pages = {{357--407}}, publisher = {{IOP Publishing}}, title = {{{Time-dependent density-functional theory for extended systems}}}, doi = {{10.1088/0034-4885/70/3/r02}}, volume = {{70}}, year = {{2007}}, } @article{18591, abstract = {{Using density-functional theory, we investigate the stability of the half-metallic ground state of magnetite under different strain conditions. The effects of volume relaxation and internal degrees of freedom are fully taken into account. For hydrostatic compression, planar strain in the (001) plane and uniaxial strain along the [001] direction, we derive quantitative limits beyond which magnetite becomes metallic. As a major new result, we identify the bond length between the octahedrally coordinated iron atoms and their neighbouring oxygen atoms as the main characteristic parameter, and we show that the transition occurs if external strain reduces this interatomic distance from 2.06 Å in equilibrium to below a critical value of 1.99 Å. Based on this criterion, we also argue that planar strain due to epitaxial growth does not lead to a metallic state for magnetite films grown on (111)-oriented substrates.}}, author = {{Friák, Martin and Schindlmayr, Arno and Scheffler, Matthias}}, issn = {{1361-6633}}, journal = {{New Journal of Physics}}, number = {{1}}, publisher = {{IOP Publishing and Deutsche Physikalische Gesellschaft}}, title = {{{Ab initio study of the half-metal to metal transition in strained magnetite}}}, doi = {{10.1088/1367-2630/9/1/005}}, volume = {{9}}, year = {{2007}}, } @inbook{18593, abstract = {{We present a quantitative parameter-free method for calculating defect states and charge-transition levels of point defects in semiconductors. It combines the strength of density-functional theory for ground-state total energies with quasiparticle corrections to the excitation spectrum obtained from many-body perturbation theory. The latter is implemented within the G0W0 approximation, in which the electronic self-energy is constructed non-self-consistently from the Green’s function of the underlying Kohn–Sham system. The method is general and applicable to arbitrary bulk or surface defects. As an example we consider anion vacancies at the (110) surfaces of III–V semiconductors. Relative to the Kohn–Sham eigenvalues in the local-density approximation, the quasiparticle corrections open the fundamental band gap and raise the position of defect states inside the gap. As a consequence, the charge-transition levels are also pushed to higher energies, leading to close agreement with the available experimental data.}}, author = {{Schindlmayr, Arno and Scheffler, Matthias}}, booktitle = {{Theory of Defects in Semiconductors}}, editor = {{Drabold, David A. and Estreicher, Stefan K.}}, isbn = {{978-3-540-33400-2}}, issn = {{1437-0859}}, pages = {{165--192}}, publisher = {{Springer}}, title = {{{Quasiparticle calculations for point defects at semiconductor surfaces}}}, doi = {{10.1007/11690320_8}}, volume = {{104}}, year = {{2007}}, } @article{18595, abstract = {{Excited-state calculations, notably for quasiparticle band structures, are nowadays routinely performed within the GW approximation for the electronic self-energy. Nevertheless, certain numerical approximations and simplifications are still employed in practice to make the computations feasible. An important aspect for periodic systems is the proper treatment of the singularity of the screened Coulomb interaction in reciprocal space, which results from the slow 1/r decay in real space. This must be done without introducing artificial interactions between the quasiparticles and their periodic images in repeated cells, which occur when integrals of the screened Coulomb interaction are discretised in reciprocal space. An adequate treatment of both aspects is crucial for a numerically stable computation of the self-energy. In this article we build on existing schemes for isotropic screening and present an extension for anisotropic systems. We also show how the contributions to the dielectric function arising from the non-local part of the pseudopotentials can be computed efficiently. These improvements are crucial for obtaining a fast convergence with respect to the number of points used for the Brillouin zone integration and prove to be essential to make GW calculations for strongly anisotropic systems, such as slabs or multilayers, efficient.}}, author = {{Freysoldt, Christoph and Eggert, Philipp and Rinke, Patrick and Schindlmayr, Arno and Godby, Rex W. and Scheffler, Matthias}}, issn = {{0010-4655}}, journal = {{Computer Physics Communications}}, number = {{1}}, pages = {{1--13}}, publisher = {{Elsevier}}, title = {{{Dielectric anisotropy in the GW space–time method}}}, doi = {{10.1016/j.cpc.2006.07.018}}, volume = {{176}}, year = {{2007}}, } @inbook{18601, author = {{Friedrich, Christoph and Schindlmayr, Arno}}, booktitle = {{Computational Condensed Matter Physics}}, editor = {{Blügel, Stefan and Gompper, Gerhard and Koch, Erik and Müller-Krumbhaar, Heiner and Spatschek, Robert and Winkler, Roland G.}}, isbn = {{3-89336-430-7}}, issn = {{1433-5506}}, location = {{Jülich}}, pages = {{A5.1--A5.21}}, publisher = {{Forschungszentrum Jülich}}, title = {{{Many-body perturbation theory: The GW approximation}}}, volume = {{32}}, year = {{2006}}, } @inbook{18603, author = {{Schindlmayr, Arno}}, booktitle = {{Computational Condensed Matter Physics}}, editor = {{Blügel, Stefan and Gompper, Gerhard and Koch, Erik and Müller-Krumbhaar, Heiner and Spatschek, Robert and Winkler, Roland G.}}, isbn = {{3-89336-430-7}}, issn = {{1433-5506}}, location = {{Jülich}}, pages = {{A4.1--A4.19}}, publisher = {{Forschungszentrum Jülich}}, title = {{{Time-dependent density-functional theory}}}, volume = {{32}}, year = {{2006}}, } @inbook{18606, abstract = {{In this lecture we present many-body perturbation theory as a method to determine quasiparticle excitations in solids, especially electronic band structures, accurately from first principles. The main ingredient is the electronic self-energy that, in principle, contains all many-body exchange and correlation effects beyond the Hartree potential. As its exact mathematical expression is unknown, approximations must be used in practical calculations. The approximation is obtained using a systematic algebraic approach on the basis of Green function techniques. It constitutes an expansion of the self-energy up to linear order in the screened Coulomb potential, which describes the interaction between the quasiparticles and includes dynamic screening through the creation of exchange-correlation holes around the bare particles. The implementation of the approximation relies on a perturbative treatment starting from density functional theory. Besides a detailed mathematical discussion we focus on the underlying physical concepts and show some illustrative applications.}}, author = {{Friedrich, Christoph and Schindlmayr, Arno}}, booktitle = {{Computational Nanoscience: Do It Yourself!}}, editor = {{Grotendorst, Johannes and Blügel, Stefan and Marx, Dominik}}, isbn = {{3-00-017350-1}}, location = {{Jülich}}, pages = {{335--355}}, publisher = {{John von Neumann Institute for Computing}}, title = {{{Many-body perturbation theory: The GW approximation}}}, volume = {{31}}, year = {{2006}}, } @article{18597, abstract = {{We propose a new method for calculating optical defect levels and thermodynamic charge-transition levels of point defects in semiconductors, which includes quasiparticle corrections to the Kohn-Sham eigenvalues of density-functional theory. Its applicability is demonstrated for anion vacancies at the (110) surfaces of III–V semiconductors. We find the (+/0) charge-transition level to be 0.49 eV above the surface valence-band maximum for GaAs(110) and 0.82 eV for InP(110). The results show a clear improvement over the local-density approximation and agree closely with an experimental analysis.}}, author = {{Hedström, Magnus and Schindlmayr, Arno and Schwarz, Günther and Scheffler, Matthias}}, issn = {{1079-7114}}, journal = {{Physical Review Letters}}, number = {{22}}, publisher = {{American Physical Society}}, title = {{{Quasiparticle corrections to the electronic properties of anion vacancies at GaAs(110) and InP(110)}}}, doi = {{10.1103/PhysRevLett.97.226401}}, volume = {{97}}, year = {{2006}}, } @article{18599, abstract = {{This paper investigates the influence of the basis set on the GW self-energy correction in the full-potential linearized augmented-plane-wave (LAPW) approach and similar linearized all-electron methods. A systematic improvement is achieved by including local orbitals that are defined as second and higher energy derivatives of solutions to the radial scalar-relativistic Dirac equation and thus constitute a natural extension of the LAPW basis set. Within this approach linearization errors can be eliminated, and the basis set becomes complete. While the exchange contribution to the self-energy is little affected by the increased basis-set flexibility, the correlation contribution benefits from the better description of the unoccupied states, as do the quasiparticle energies. The resulting band gaps remain relatively unaffected, however; for Si we find an increase of 0.03 eV.}}, author = {{Friedrich, Christoph and Schindlmayr, Arno and Blügel, Stefan and Kotani, Takao}}, issn = {{1550-235X}}, journal = {{Physical Review B}}, number = {{4}}, title = {{{Elimination of the linearization error in GW calculations based on the linearized augmented-plane-wave method}}}, doi = {{10.1103/physrevb.74.045104}}, volume = {{74}}, year = {{2006}}, } @inbook{18608, author = {{Schindlmayr, Arno}}, booktitle = {{Magnetism goes Nano}}, editor = {{Blügel, Stefan and Brückel, Thomas and Schneider, Claus Michael}}, isbn = {{3-89336-381-5}}, issn = {{1433-5506}}, location = {{Jülich}}, pages = {{D1.1--D1.20}}, publisher = {{Forschungszentrum Jülich}}, title = {{{Magnetic excitations}}}, volume = {{26}}, year = {{2005}}, } @article{18610, abstract = {{We discuss the implementation of quasiparticle calculations for point defects on semiconductor surfaces and, as a specific example, present an ab initio study of the electronic structure of the As vacancy in the +1 charge state on the GaAs(110) surface. The structural properties are calculated with the plane‐wave pseudopotential method, and the quasiparticle energies are obtained from Hedin's GW approximation. Our calculations show that the 1a″ vacancy state in the band gap is shifted from 0.06 to 0.65 eV above the valence‐band maximum after the self‐energy correction to the Kohn‐Sham eigenvalues. The GW result is in close agreement with a recent surface photovoltage imaging measurement.}}, author = {{Hedström, Magnus and Schindlmayr, Arno and Scheffler, Matthias}}, issn = {{1521-3951}}, journal = {{Physica Status Solidi B}}, number = {{1}}, pages = {{346--353}}, publisher = {{Wiley-VCH}}, title = {{{Quasiparticle calculations for point defects on semiconductor surfaces}}}, doi = {{10.1002/1521-3951(200211)234:1%3C346::AID-PSSB346%3E3.0.CO;2-J}}, volume = {{234}}, year = {{2002}}, } @article{18612, abstract = {{There is increasing interest in many-body perturbation theory as a practical tool for the calculation of ground-state properties. As a consequence, unambiguous sum rules such as the conservation of particle number under the influence of the Coulomb interaction have acquired an importance that did not exist for calculations of excited-state properties. In this paper we obtain a rigorous, simple relation whose fulfilment guarantees particle-number conservation in a given diagrammatic self-energy approximation. Hedin’s G0W0 approximation does not satisfy this relation and hence violates the particle-number sum rule. Very precise calculations for the homogeneous electron gas and a model inhomogeneous electron system allow the extent of the nonconservation to be estimated.}}, author = {{Schindlmayr, Arno and García-González, Pablo and Godby, Rex William}}, issn = {{1095-3795}}, journal = {{Physical Review B}}, number = {{23}}, publisher = {{American Physical Society}}, title = {{{Diagrammatic self-energy approximations and the total particle number}}}, doi = {{10.1103/PhysRevB.64.235106}}, volume = {{64}}, year = {{2001}}, } @article{18615, abstract = {{The performance of several common approximations for the exchange-correlation kernel within time-dependent density-functional theory is tested for elementary excitations in the homogeneous electron gas. Although the adiabatic local-density approximation gives a reasonably good account of the plasmon dispersion, systematic errors are pointed out and traced to the neglect of the wave-vector dependence. Kernels optimized for atoms are found to perform poorly in extended systems due to an incorrect behavior in the long-wavelength limit, leading to quantitative deviations that significantly exceed the experimental error bars for the plasmon dispersion in the alkali metals.}}, author = {{Tatarczyk, Krzysztof and Schindlmayr, Arno and Scheffler, Matthias}}, issn = {{1095-3795}}, journal = {{Physical Review B}}, number = {{23}}, publisher = {{American Physical Society}}, title = {{{Exchange-correlation kernels for excited states in solids}}}, doi = {{10.1103/PhysRevB.63.235106}}, volume = {{63}}, year = {{2001}}, } @inbook{18614, author = {{Schindlmayr, Arno}}, booktitle = {{Recent Research Developments in Physics}}, editor = {{Pandalai, S. G.}}, isbn = {{81-7895-024-3}}, pages = {{277--288}}, publisher = {{Transworld Research Network}}, title = {{{Self-consistency and vertex corrections beyond the GW approximation}}}, volume = {{2}}, year = {{2001}}, }