Search query: First-principles determination of defect energy levels through hybrid density functionals and GW

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abstract: In this topical review, we discuss recent progress in electronic structure methods for calculating defect energy levels in semiconductors and insulators. We concentrate mainly on two advanced electronic structure schemes, namely hybrid density functional theory and many body perturbation theory in the GW approximation. These two schemes go beyond standard density functional theory in the semilocal approximation providing a more realistic description of band gaps. In particular, we address important aspects underlying the GW scheme and highlight the correspondence between the defect levels as obtained in the various schemes. We further assess the quality of the band edge positions determined with hybrid functionals and GW through the calculation of band offsets at semiconductor heterojunctions and of ionization potentials at semiconductor surfaces.
author_names: Wei Chen

Alfredo Pasquarello
title: First principles determination of defect energy levels through hybrid density functionals and GW.
venue: Journal of physics. Condensed matter an Institute of Physics journal
year: 2015

abstract: This work presents an in depth investigation of the properties of complexes composed of hydrogen, silicon, or oxygen with carbon, which are the major unintentional impurities in undoped GaN. This manuscript is a complement to our previous work on carbon carbon and carbon vacancy complexes. We have employed a first principles method using Heyd Scuseria Ernzerhof hybrid functionals within the framework of generalized Kohn Sham density functional theory. Two H C, four Si C, and five O C complexes in different charge states have been considered. After full geometry relaxations, formation energies, binding energies, and both thermal and optical transition levels were obtained. The calculated energy levels have been systematically compared with the experimentally observed carbon related trap levels. Furthermore, we computed vibrational frequencies for selected defect complexes and defect concentrations were estimated in the low, mid, and high carbon doping scenarios considering two different cases where electri.
author_names: Masahiko Matsubara

Enrico Bellotti
title: A first principles study of carbon related energy levels in GaN. II. Complexes formed by carbon and hydrogen, silicon or oxygen
year: 2017

abstract: I demonstrate that the ionization energy (IE) and the electron affinity (EA) of organic molecular crystals can be predicted from first principles. Here, I describe the induced electronic polarization and the electrostatic effects upon crystalline IE and EA. I also demonstrate that the electronic polarization mainly originates from the screened coulomb interaction inside the crystalline bulk phase, and that the electrostatic contribution to IE and EA crucially depends on the orientation of the molecule at the surface. The former is well described by the GW approximation, while the latter is reasonably estimated by the difference in frontier orbital energy between the gas phase and the surface at the level of a generalized gradient approximation to the density functional theory. The present methodology enables to demonstrate the impact of the electrostatic effect upon the energy level of the injected charge at a multi monolayer surface of an organic semiconductor thin film.
author_names: Susumu Yanagisawa
title: Determination of the ionization energy and the electron affinity of organic molecular crystals from first principles: dependence on the molecular orientation at the surface
year: 2020

abstract: Abstract Zinc sulfide (ZnS) based materials are widely used in many applications. Yet, due to a lack of detailed knowledge of defect energy levels, the electrical properties and luminescence mechanisms in the materials still give rise to debate. Here, we report a first principles study of native point defects and impurities in zincblende ZnS using hybrid density functional calculations. We find that cation and anion vacancies and antisite defects introduce deep defect levels in the band gap and can act as donors or acceptors depending on the position of the Fermi level. The substitutional impurity Cu Zn acts as a deep acceptor and thus does not contribute to p type conductivity. Substitutional impurities Al Zn and Cl S on the other hand, are shallow donors. More importantly, we identify the isolated (i.e. unassociated) Cu Zn as a source of the green luminescence observed in ZnS based phosphors and Cu Zn Al Zn and Cu Zn Cl S defect complexes as sources of blue luminescence. The materials may have both green and blue emissions with the relative intensity dependent on the ratio between the unassociated defect and defect complex concentrations, which is also consistent with experimental observations.
author_names: Khang Hoang

Camille Latouche

Stephane Jobic
title: Defect energy levels and persistent luminescence in Cu doped ZnS
venue: Computational Materials Science
year: 2019

abstract: Calculations of formation energies and charge transition levels of defects routinely rely on density functional theory (DFT) for describing the electronic structure. Since bulk band gaps of semiconductors and insulators are not well described in semilocal approximations to DFT, band gap correction schemes or advanced theoretical models, which properly describe band gaps, need to be employed. However, it has become apparent that different methods that reproduce the experimental band gap can yield substantially different results regarding charge transition levels of point defects. We investigate this problem in the case of the +2/0) charge transition level of the O vacancy in ZnO, which has attracted considerable attention as a benchmark case. For this purpose, we first perform calculations based on nonscreened hybrid density functionals, and then compare our results with those of other methods. While our results agree very well with those obtained with screened hybrid functionals, they are strikingly different compared to those obtained with other band gap corrected schemes. Nevertheless, we show that all the different methods agree well with each other and with our calculations when a suitable alignment procedure is adopted. The proposed procedure consists in aligning the electron band structure through an external potential, such as the vacuum level. When the electron densities are well reproduced, this procedure is equivalent to an alignment through the average electrostatic potential in a calculation subject to periodic boundary conditions. We stress that, in order to give accurate defect levels, a theoretical scheme is required to yield not only band gaps in agreement with experiment, but also band edges correctly positioned with respect to such a reference potential.
author_names: Audrius Alkauskas

Alfredo Pasquarello
title: Band edge problem in the theoretical determination of defect energy levels: The O vacancy in ZnO as a benchmark case
year: 2011

abstract: Owing to the increasing popularity of lead based hybrid perovskites for photovoltaic (PV) applications, it is crucial to understand their defect physics and its influence on their optoelectronic properties. In this work, we simulate various point defects in pseudo cubic structures of mixed iodide bromide and bromide chloride methylammonium lead perovskites with the general formula MAPbI_{3 y}Br_{y} or MAPbBr_{3 y}Cl_{y} (where y is between 0 and 3) and use first principles based density functional theory computations to study their relative formation energies and charge transition levels. We identify vacancy defects and Pb on MA anti site defect as the lowest energy native defects in each perovskite. We observe that while the low energy defects in all MAPbI_{3 y}Br_{y} systems only create shallow transition levels, the Br or Cl vacancy defects in the Cl containing pervoskites have low energy and form deep levels which become deeper for higher Cl content. Further, we study extrinsic substitution by different elements at the Pb site in MAPbBr_{3} MAPbCl_{3} and the 50 50 mixed halide perovskite, MAPbBr_{1.5}Cl_{1.5} and identify some transition metals that create lower energy defects than the dominant intrinsic defects and also create mid gap charge transition levels.
author_names: Arun Mannodi-Kanakkithodi

Ji-Sang Park

Alex B F Martinson

Maria K Y Chan
title: Defect Physics of Pseudo cubic Mixed Halide Lead Perovskites from First Principles.
year: 2019

abstract: The accuracy of $GW$ in the determination of defect energy levels is assessed through calculations on a set of well characterized point defects in semiconductors: the As antisite in GaAs, the substitutional Mg in GaN, the interstitial C in Si, the Si dangling bond, and the Si split vacancy complex in diamond. We show that the $GW$ scheme achieves a reliable description of charge transition levels, but the overall accuracy is comparable to that of hybrid functional calculations.
author_names: Wei Chen

Alfredo Pasquarello
title: Accuracy of G W for calculating defect energy levels in solids
year: 2017

abstract: Hybrid density functional calculations applied to defect charge transition levels are explored in the attempt to overcome the band gap problem of semilocal density functionals. Charge transition levels of a large set of point defects calculated with semilocal and hybrid density functionals are found to correspond closely when aligned with respect to the average electrostatic potential. This strongly suggests that the defect levels defined in this way are already accurately described at these levels of theory. In particular, this then also applies to the energy separation between different defect levels, which is directly accessible experimentally. At variance, within the same alignment scheme, the band edges obtained with hybrid functionals are found to undergo significant shifts with respect to those obtained with semilocal functionals. While these shifts systematically give larger band gaps, the agreement with experiment is not always satisfactory when a fixed fraction of exact exchange is admixed. This describes a current limitation of hybrid functional schemes. In the attempt of identifying a viable theoretical description within the class of one parameter hybrid functionals based on bare exchange, we explore the validity of the empirical procedure which consists in tuning the fraction of nonlocal exchange to a value which gives a theoretical band gap reproducing the experimental one. Comparisons with experiment for band offsets and specific defect levels record very encouraging results. Despite its inherent limitations, such an empirical scheme based on hybrid functionals represents a definite improvement with respect to semilocal functionals.
author_names: Audrius Alkauskas

Peter Broqvist

Alfredo Pasquarello
title: Defect Levels Through Hybrid Density Functionals: Insights and Applications
year: 2011

abstract: Abstract First principles calculations based on density functional theory (DFT) have been performed for layered 2H tungsten disulphide (WS2) with the aim to find its possible applications in opto electronic and hydrogen storage devices. To study opto electronic features of WS2, we solve the Bethe Salpeter Equation (BSE) on top of the standard self consistent GW quasiparticle (QP) calculations. These calculations capture the excitonic effects which originate near the edge of conduction band, shows good agreement with the available measured data. The suitability of WS2 as a prospective material for hydrogen storage were predicted by using the Heyd Scuseria Ernzerhof (HSE06) hybrid functional. We have explored the effect of interstitial hydrogen and H2 molecules insertion on the structural stability of WS2 in detail. The hydrogen atom charge states dependent stability was studied in the context of formation energy. Our calculations suggest that interstitial hydrogen can act as a deep donor whereas H2 molecule exhibits more stability. The diffusion energy of H2 molecule from one hollow site to the nearest in plane hollow site has been calculated using transition state theory. Finally, ab initio molecular dynamics (AIMD) calculations are carried out for WS2 consisting of 16H2 molecules that ensures its structural stability at temperatures 300, 500, and 1000 K. Present predictions show that this material may be utilize for hydrogen storage due to expected high hydrogen density.
author_names: D K Sharma

Surajit Kumar

Sushil Auluck
title: Electronic structure, defect properties, and hydrogen storage capacity of 2H WS2: A first principles study
year: 2018

abstract: We have employed first principles total energy calculations in the framework of density functional theory, with plane wave basis sets and screened exchange hybrid functionals to study the incorporation of intrinsic defects in bulk b In2S3. The results are obtained for In rich and S rich experimental growth conditions. The charge transition level is discussed for all native defects, including VIn, VS, Ini, Si, SIn, and InS, and a comparison between the theoretically calculated charge transition levels and the available experimental findings is presented. The results imply that b In2S3 shows n type conductivity under both In rich and S rich growth conditions. The indium antiisite (InS) the indium interstitial (Ini) and the sulfur vacancy VS' are found to be the leading sources of sample's n type conductivity. When going from the In rich to the S rich condition, the conductivity of the material decreases; however, the type of conductivity remains unchanged.
author_names: Elaheh Ghorbani

Karsten Albe
title: Intrinsic point defects in b In2S3 studied by means of hybrid density functional theory
year: 2018