First-principles modeling of localized d states with the GW@LDA+U approach

First-principles modeling of systems with localized d states is currently a great challenge in condensed-matter physics. Density-functional theory in the standard local-density approximation (LDA) proves to be problematic. This can be partly overcome by including local Hubbard U corrections (LDA+U) but itinerant states are still treated on the LDA level. Many-body perturbation theory in the GW approach offers both a quasiparticle perspective (appropriate for itinerant states) and an exact treatment of exchange (appropriate for localized states), and is therefore promising for these systems. LDA+U has previously been viewed as an approximate GW scheme. We present here a derivation that is simpler and more general, starting from the static Coulomb-hole and screened exchange approximation to the GW self-energy. Following our previous work for f-electron systems [H. Jiang, R.I. Gomez-Abal, P. Rinke, and M. Scheffler, Phys. Rev. Lett. 102, 126403 (2009)] we conduct a systematic investigation of the GW method based on LDA+U(GW@LDA+U), as implemented in our recently developed all-electron GW code FHI-gap (Green’s function with augmented plane waves) for a series of prototypical d-electron systems: (1) ScN with empty d states, (2) ZnS with semicore d states, and (3) late transition-metal oxides (MnO, FeO, CoO, and NiO) with partially occupied d states. We show that for ZnS and ScN, the GW band gaps only weakly depend on U but for the other transition-metal oxides the dependence on U is as strong as in LDA+U. These different trends can be understood in terms of changes in the hybridization and screening. Our work demonstrates that GW@LDA+U with "physical" values of U provides a balanced and accurate description of both localized and itinerant states

Electronic band structure of zirconia and hafnia polymorphs from the GW perspective

The electronic structure of crystalline ZrO2 and HfO2 in the cubic, tetragonal, and monoclinic phase has been investigated using many-body perturbation theory in the GW approach based on density-functional theory calculations in the local-density approximation (LDA). ZrO2 and HfO2 are found to have very similar quasiparticle band structures. Small differences between them are already well described at the LDA level indicating that the filled f shell in HfO2 has no significant effect on the GW corrections. A comparison with direct and inverse photoemission data shows that the GW density of states agrees very well with experiment. A systematic investigation into the structural and morphological dependence of the electronic structure reveals that the internal displacement of the oxygen atoms in the tetragonal phase has a significant effect on the band gap

Aplicabilidad de las herramientas de ayuda a la toma de decisiones compartidas en los servicios de Urgencias: una revisión exploratoria

Fundamentos: Las herramientas de ayuda en la toma de decisiones (HATD) han sido muy utilizadas en las enfermedades crónicas, pero existen pocos estudios sobre su utilidad en los servicios de urgencias. El objetivo de este estudio fue analizar la utilización de las HATD en los servicios de urgencias. Métodos: Se realizó una revisión exploratoria. Se realizaron búsquedas de ensayos clínicos aleatorizados y controlados, revisiones sistemáticas y otros estudios se-cundarios donde se utilizaran las HATD para la asistencia a pacientes de cualquier edad en los servicios de urgen-cias, entre el 1 de enero de 2012 y el 1 de agosto de 2019. Dos revisores examinaron y seleccionaron los estudios. Se utilizaron las siguientes bases de datos: Pubmed, Embase, Web Of Science, Cuiden, Patient Decision Aids Research Group IPDAS Collaboration, Cochrane, Centres for Reviews and Dissemination, National Guideline Clearinghouse, Guidelines International Network. Resultados: Se incluyeron doce estudios, de calidad metodológica moderada-baja. Los pacientes del Grupo de Intervención (GI) tenían mayor conocimiento de la enfer-medad (?=3, 6 frente a 3 preguntas correctas y ?=4, 2 frente a 3, 6) y más implicación en las decisiones (puntuación en OPTION: 26, 6 contra 7 y 18, 3 contra 7). El conflicto se redujo en el GI en las decisiones sobre pruebas de imagen en el traumatismo craneoencefálico (TCE) (?=14, 8 frente a 19, 2). En el GI era menos frecuente el ingreso para realizar una prueba de esfuerzo en casos de dolor torácico de bajo riesgo (58% contra 77%; IC95%=6%-31%, y 37% contra 52%; p<0, 001). Cuando se utilizaba una HATD en niños con diarrea o vómitos, en el 80% la decisión era seguir una rehidratación oral frente al 61% en el GC (p=0, 001). Conclusiones: Las HATD en los servicios de urgen-cias mejoran el conocimiento de los pacientes sobre la en-fermedad y la participación en los cuidados. Se necesitan más estudios para desarrollar HATD en los servicios de urgencias. Background: Decision aid tools (DAT) have been widely used in chronic diseases, but there are few studies on their usefulness in emergency departments. The objective of this study was to analyse the applicability of DAT in emergency services. Methods: An exploratory review was conducted. Between January 1, 2012 and August 1, 2019, searches of randomised and controlled clinical trials, systematic reviews and other secondary studies where DAT are used to assist patients of any age in emergency services were conducted. The databases used were: Pubmed, Embase, Web Of Science, Cuiden, Patient Decision Aids Research Group IPDAS Collaboration, Cochrane, Centres for Reviews and Dissemination, National Guideline Clearinghouse, Guidelines International Network. Two reviewers analysed and selected the studies. Results: Twelve studies of moderate-low quality were included. The patients in the intervention group (IG) were more aware of their illness ((X) over bar =3.6 vs 3 correct answers and (X) over bar =4.2 vs 3.6), and more involved in the decisions (score in OPTION: 26.6 vs 7 and 18.3 vs 7). The conflict was reduced in the IG regarding those imaging tests in the TBI (traumatic brain injury; (X) over bar =14.8 vs 19.2). In the IG, admittance to perform effort tests was reduced in low-risk chest pain (58% vs 77%; CI95%=6%-31%, 37% vs 52%; p<0.001). When DAT were used in children with diarrhoea or vomiting, in 80% of the cases the decision was to use oral rehydration against 61% in the control group (CG, p=0.001). Conclusions: DAT in emergency services improve patient''s knowledge about the disease and their participation in care. More studies are needed to develop DAT in emergency services

On the Chemical Origin of the Gap Bowing in (GaAs)1−xGe2x Alloys: A Combined DFT–QSGW Study

Motivated by the research and analysis of new materials for photovoltaics and by the possibility of tailoring their optical properties for improved solar energy conversion, we have focused our attention on the (GaAs)1−xGe2x series of alloys. We have investigated the structural properties of some (GaAs)1−xGe2x compounds within the local-density approximation to density-functional theory, and their optical properties within the Quasiparticle Self-consistent GW approximation. The QSGW results confirm the experimental evidence of asymmetric bandgap bowing. It is explained in terms of violations of the octet rule, as well as in terms of the order–disorder phase transition

Impact of widely used approximations to the G₀W₀ method: an all-electron perspective

Focusing on the fundamental band gaps in Si, diamond, BN, LiF, AlP, NaCl, CaSe and GaAs, and the semicore d-state binding energies in ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe and GaN, we study the differences between the all-electron (AE) G0W0G0W0 method. Leaving aside issues related to the choice of PPs within PP-G0W0, we analyze in detail the well-known discrepancies between AE-G0W0 and PP-G0W0 band gaps by separately addressing the approximations underlying PP-G0W0, i.e. the frozen-core approximation, the core–valence partitioning and the use of pseudo-wavefunctions. The largest differences, of the order of eV, appear in the exchange part of the self-energy and the exchange–correlation potential due to the core–valence partitioning. These differences cancel each other and, in doing so, make the final core–valence partitioning effect on the band gaps controllable when the semicore states are treated as valence states. This cancelation, however, is incomplete for semicore d-state binding energies, due to the strong interaction between these semicore states and the deep core. From our comprehensive analysis, we conclude that reliably describing the many-body interactions at the G0W0 level and providing benchmark results require an AE treatment

FHI-gap: A GW code based on the all-electron augmented plane wave method

The GW method has become the state-of-the-art approach for the first-principles description of the electronic quasi-particle band structure in crystalline solids. Most of the existing codes rely on pseudopotentials in which only valence electrons are treated explicitly. The pseudopotential method can be problematic for systems with localized d- or f -electrons, even for ground-state density-functional theory (DFT) calculations. The situation can become more severe in GW calculations, because pseudowavefunctions are used in the computation of the self-energy and the core–valence interaction is approximated at the DFT level. In this work, we present the package FHI-gap, an all-electron GW implementation based on the full-potential linearized augmented planewave plus local orbital (LAPW) method. The FHI-gap code can handle core, semicore, and valence states on the same footing, which allows for a correct treatment of core–valence interaction. Moreover, it does not rely on any pseudopotential or frozen-core approximation. It is, therefore, able to handle a wide range of materials, irrespective of their composition. Test calculations demonstrate the convergence behavior of the results with respect to various cut-off parameters. These include the size of the basis set that is used to expand the products of Kohn–Sham wavefunctions, the number of k points for the Brillouin zone integration, the number of frequency points for the integration over the imaginary axis, and the number of unoccupied states. At present, FHI-gap is linked to the WIEN2k code, and an implementation into the exciting code is in progress