DOCSLIB.ORG

Full Spectrum Optical Constant Interface to the Materials Project

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Full Spectrum Optical Constant Interface to the Materials Project Full spectrum optical constant interface to the Materials Project J. J. Kasa,b, F. D. Vilaa,b, C. D. Pemmarajub, M. P. Prangec, K. A. Perssond, R. X. Yangd, J. J. Rehra,b,∗ aDepartment of Physics, University of Washington, Seattle, WA 98195, USA bStanford Institute for Materials and Energies Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA cPhysical and Computational Sciences Directorate, Pacific Northwest National Laboratory: Richland, WA 99352 dMaterials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA Abstract Optical constants characterize the interaction of materials with light and are important properties in material design. Here we present a Python-based Corvus workflow for simulations of full spectrum optical constants from the UV- VIS to hard x-ray wavelengths based on the real-space Green's function code FEFF10 and structural data from the Materials Project (MP). The Corvus workflow manager and its associated tools provide an interface to FEFF10 and the MP database. The workflow parallelizes the FEFF computations of optical constants over all absorption edges for each material in the MP database specified by a unique MP-ID. The workflow tools determine the distribution of computational resources needed for that case. Similarly, the optical constants for selected sets of materials can be computed in a single-shot. To illustrate the approach, we present results for nearly all elemental solids in the periodic table, as well as a sample compound, and compared with experimental results. As in x-ray absorption spectra, these results are interpreted in terms of an atomic-like background and fine-structure contributions. Keywords: Optical constants, Materials Project, FEFF, Corvus 1. Introduction quantitative.[8{17] Also limited tables of theoretical op- tical constants of materials have been compiled over the Optical constants characterize the frequency depen- optical range.[18, 19] However, such calculations involve dent interaction between light and matter in the long- many-body calculations of optical response, and become wavelength limit. Thus they are often important char- computationally intractable for many materials over broad acteristics in materials design. These properties include spectral ranges. In contrast, the real-space Green's func- the complex dielectric constant and index of refraction, tion (RSGF) approach in FEFF10 includes the key many- as well as the energy-loss function, photoabsorption co- body effects, is highly automated and has proved to be efficient, and optical reflectivity.[1{4] Many other physi- quite accurate for general materials in the x-ray regime. cal properties can be derived from the optical constants, Moreover the code can be semi-quantitative in the UV-VIS including electron energy loss spectra (EELS), inelastic to soft-x-ray regime.[20] Thus the code provides an effi- mean-free paths, the atomic scattering amplitudes, and cient platform for calculations of dielectric properties over Hamaker constants for the van der Waals interaction. For a broad spectral range. Consequently, theoretical calcula- these purposes, tabulations of experimentally determined tions based on FEFF10 provide an attractive alternative to optical constants are widely used.[1{4] For practical rea- available theoretical and experimental tabulations of op- sons, however, such tabulations are limited to a rela- tical constants for many purposes. Nevertheless, selected tively small number of well characterized materials over experimental measurements are important to validate the limited spectral ranges and limited environmental condi- theory. tions. Thus here we focus on broad spectrum theoreti- cal treatments for the systems defined in the Materials Recently K- and L-shell XAS calculations based on the Project(MP) database. FEFF code have been added for a very large number of Significant progress has been made in the fundamen- materials in the Materials Project (MP) database.[21, 22] arXiv:2108.10981v2 [cond-mat.mtrl-sci] 26 Aug 2021 tal theory of optical properties since the pioneering These data have been exploited, e.g., in machine-learning works of Nozieres and Pines,[5] Adler,[6] and Wiser.[7] models for the interpretation of XAS data.[21, 23] Our In particular modern first-principles calculations based aim here is to complement these properties with a more on time-dependent density functional theory (TDDFT) complete set of optical constants for all edges from the and the Bethe-SalpeterEquation (BSE) are now highly UV-VIS to hard-x-ray energies. Consequently, the results presented here provide significant extension, both in the ∗Corresponding author variety of optical-constant spectra, spectral range, and ma- Email address: [email protected] (J. J. Rehr) terial properties. Our approach is based on the the devel- Preprint submitted to Computational Materials Science August 27, 2021 1e4 opment of the Corvus [opcons] workflow, where Corvus is Expt. (DESY) the workflow engine,[24] and opcons is the target property. FEFF (Opcons) 2 atomic In particular, the approach imports the structural and 1e property data from the MP, and then parallelizes and au- 1e0 tomates the calculations permitting high-throughput cal- culations of optical constants for materials throughout the 1e−2 MP database. Our procedure for theoretical calculations (E) 2 ε of optical constants over all edges essentially follows that 1e−4 Cu described in detail by Prange et al.,[20] but has been up- dated for the FEFF10 code. In addition, refinements for 1e−6 including vibrational disorder via the correlated Debye −8 model using MP data have been added and the calcula- 1e tions for the UV-VIS range have been simplified. To il- 1e−10 lustrate the approach calculations have been carried out 0.1 1 10 100 1000 10000 100000 for nearly all elemental solids throughout the periodic ta- Energy (eV) ble and explicit examples are given for Cu, Ag, and Au, 0.7 full together with comparisons to experimental data. In ad- L−edges 0.6 K−edge dition we show results for a sample compound Al2O3 to validate our approximation in the UV-VIS range. The 0.5 Corvus workflow described here is applicable to [opcons] 0.4 any material available in the MP database as defined by a given MP identificatoin label (MP-ID), thus making pos- 0.3 (E) 5 χ sible routine calculations of optical constants for over 10 0.2 structures. By default, the calculations are carried out with lattice vibration effects included at room tempera- 0.1 ture, while electronic temperature and thermal expansion 0 effects are neglected. However, corrections for thermal ex- pansion, finite temperature, and pressures other than 1 −0.1 atm can be added using subsequent calculations that reuse 2 4 6 8 10 12 14 some of the previously computed data. The workflow is k(E) (Å) naturally parallelized and, for typical settings, requires as little as minutes of wall-clock time per material on mas- Figure 1: Top: Calculated imaginary part of the dielectric function sively parallel systems. 2 for Cu (blue) along with the atomic background χ (see text) (red). Bottom: Approximate opticalp fine structure of the imaginary (blue) part of for Cu vs k = 2E, along with the same fine-structure defined with energies E relative to the K- and L-edges. Note the similarities between the fine structure found in the optical and that of the K-edge. Note also that the fine structure becomes negligible for large k above any edges or outside the optical range. terms of 2(!), 2. Optical constants with Corvus and FEFF10 Z 1 0 0 2 0 ! 2(! ) 1(!) = 1 + P d! 2 02 (1) π 0 ! − ! −1 2(!) L(!) = −Im[ (!)] = 2 2 (2) 1(!) + 2(!) n(!) = n(!) + iκ(!) = (!)1=2 (3) ! µ(!) = 2 κ(!) (4) In general, the optical constants are related to the com- c plex dielectric constant (!) = 1(!) + i2(!) in the long [n(!) − 1]2 + κ(!)2 wave-length limit, where ! is the frequency of the electro- R(!) = ; (5) [n(!) + 1]2 + κ(!)2 magnetic field. Since their real and imaginary parts are re- lated by Kramers-Kronig (KK) transformations, they can where P denotes the principal part of the integral. Note all be calculated from the imaginary part 2(!) (e.g. Fig. that at high energies dielectric response is weak, and 1). In this work the, the Corvus [opcons] workflow yields 2(!) ≈ L(!) ≈ 2κ(!) ≈ µ(!)(c=!). Sum-rules the complex dielectric function (!), energy loss function for the dielectric properties provide a qualitative check L(!), complex index of refraction n(!), absorption coef- on the reliability of the results.[25] Related properties, ficient µ(!), and reflectivity R(!) defined as follows, in such as the local atomic polarizability α(!) = ((!) − 2 1)=(4πn), the Rayleigh forward scattering amplitudes 1.8 2 2 2 f(!) = !α(!)=r0c (where r0 = e =mc is the classi- 1.6 Cu cal radius of the electron, c is the speed of light and 1.4 n = N=V is the atomic number density), electron energy loss spectra (EELS), inelastic mean-free paths, Hamaker 1.2 constants (i!), etc., can also be determined, [20] but 1 are not yet implemented in the present Corvus [opcons] 0.8 workflow. For simplicity here and below we use atomic 0.6 units e = ¯h = m = 1 throughout this paper unless other- FMS wise needed for clarity. XANES (arb. units) 0.4 Stitched MSP The treatment of excitations from the core- and valence- 0.2 FMS-MSP levels generally requires different considerations, so it is 0 convenient to separate the calculations as -0.2 8980 9000 9020 9040 9060 core val 2 = 2 + 2 ; (6) Energy (eV) core where 2 includes the contribution from all levels below a Figure 2: Cu K-edge spectrum obtained using the stitching algorithm fixed core-valence separation energy Ecv, which in FEFF10 (black). For comparison, the curves calculated using FMS (red) and is set to -40 eV.
Load more

Recommended publications
  • Poster Session 1
    POSTER SESSION I THURSDAY 10 JANUARY 2013 In alphabetical order of presenting author (underlined) Electronic structure of Co doped ZnO from the GW perspective I. Abdolhosseini Sarsari 12, C. Das Pemmaraju2, Hadi Salamati1, Stefano Sanvito2 1. Department of Physics, Isfahan University of Technology, Isfahan, 84156- 83111, Iran 2. School of Physics and CRANN, Trinity College, Dublin 2, Ireland T3 The true role of many-body polarization forces in describing the properties of liquid water Omololu Akin-Ojo1 and Krzysztof Szalewicz2 1. African University of Science and Technology, Abuja, NIGERIA 2. University of Delaware, Newark, DE, USA T5 Dispersion interactions in DFT and linear-scaling DFT Lampros Andrinopoulos1, Nicholas D. M. Hine1, Arash A. Mostofi1 1. Imperial College London T1 Theoretical studies on a gramicidin A channel using a linear-scaling DFT technique M. Arita1,2, M. Todorovic3, W. Shinoda4, D.R. Bowler5 and T. Miyazaki2,1 1. Department of Physics, Tokyo University of Science, Japan 2. Computational Materials Science Unit, National Institue for Materials Science, Japan 3. Departamento de Fisica Teorica de la Materia Condensada, Universidad Autonoma de Madrid, Madrid, Spain 4. Advanced Health Research Group, Advanced Industrial Science and Technology, Japan 5. Department of Physics & Astronomy, University College London, UK T6 Structure of liquid water from first-principles simulations with van der Waals interactions F. Corsetti1, E. Artacho1,2, J. M. Soler3, M.-V. Fern ́andez-Serra4 1CIC nanoGUNE Consolider, 20018 Donostia-San Sebasti ́an, Spain 2Dept. of Physics, University of Cambridge, Cambridge CB3 0HE, United Kingdom 3Dept. de F ́ısica de la Materia Condensada, Universidad Autonoma de Madrid, 28049 Madrid, Spain 4Dept.
    [Show full text]
  • DFT-Absorption Spectra
    2054-9 Structure and Dynamics of Hydrogen-Bonded Systems 26 - 27 October 2009 Effect of Proton Disorder on the Excited State Properties of Ice Olivia PULCI Universita' di Roma II "Tor Vergata" Dipt. di Fisica, Via della Ricerca Scientfica 1, 00133 Rome Italy EffectEffect ofof protonproton disorderdisorder onon thethe excitedexcited statestate propertiesproperties ofof iceice V. Garbuio,Garbuio M. Cascella, R. Del Sole, O. Pulci OUTLINE: •Theoretical approaches •Ice Ic(bulk) • Ice Ih surface Theoretical approaches c MBPT c c EXC W hν hν ωcv hν ωcv ωcv v v v DFT GW BSE 1) 2) 3) Ground state properties Electronic band Optical spectra structure, I, A TDDFT (Step 2) Lars Hedin 1965 Σ = iGW G: single particle Green’s function −1 W: screened Coulomb interaction = ε VW Theoretical approaches c MBPT c c EXC W hν hν ωcv hν ωcv ωcv v v v DFT GW BSE 1) 2) 3) Ground state properties Electronic band Optical spectra structure, I, A TDDFT Step 3: calculation of optical spectra within the Bethe Salpeter Equation c Absorption spectra A photon excites an electron from an occupied state to a conduction state hν e 4 4 4 4 4 PPPP=IQP +IQP Ξ v h Bethe Salpeter Equation (BSE) Kernel: Ξ v= − W e-h exchange bound excitons GWBSE ApplicableApplicable to:to: Ab-initio: (NOT “one puts nothing in, one gets nothing out”!!) •Generality, transferability 0D-3D Biological systems •Detailed physical informations •Complex theory+large comp.cost 3-D 0-D 1-D 2-D Nanowires Surfaces Nanoclusters bulks OUTLINE: •Theoretical approaches •Ic Ice (bulk) • Ice Ih surface HH2OO phasephase diagramdiagram CubicCubic iceice ((IcIc)) • It is a metastable form of ice that can be formed, by condensation of water vapor, at ambient pressure but low temperatures Cubic ice (Ic) – diamond lattice 153 K down to 113 K Studied within DFT and Tight-binding G.
    [Show full text]
  • Salpeter Equation Calculations
    Computer Physics Communications ( ) – Contents lists available at ScienceDirect Computer Physics Communications journal homepage: www.elsevier.com/locate/cpc Efficient implementation of core-excitation Bethe–Salpeter equation calculations K. Gilmore a,b,∗, John Vinson c, E.L. Shirley c, D. Prendergast d, C.D. Pemmaraju d, J.J. Kas e, F.D. Vila e, J.J. Rehr e a European Synchrotron Radiation Facility (ESRF), BP 220, F-38043 Grenoble, France b Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft Materials (FUNSOM), Soochow University, Suzhou, Jiangsu 215123, PR China c National Institute of Standards and Technology (NIST), Gaithersburg, MD 20899, USA d Molecular Foundry, Lawrence Berkeley National Lab, Berkeley, CA 94720, USA e Department of Physics, University of Washington, Seattle, WA 98195, USA article info a b s t r a c t Article history: We present an efficient implementation of the Bethe–Salpeter equation (BSE) method for obtaining Received 11 May 2015 core-level spectra including X-ray absorption (XAS), X-ray emission (XES), and both resonant and non- Received in revised form resonant inelastic X-ray scattering spectra (N/RIXS). Calculations are based on density functional theory 6 August 2015 (DFT) electronic structures generated either by abinit or Quantumespresso, both plane-wave basis, Accepted 11 August 2015 pseudopotential codes. This electronic structure is improved through the inclusion of a GW self energy. Available online xxxx The projector augmented wave technique is used to evaluate transition matrix elements between core- level and band states. Final two-particle scattering states are obtained with the NIST core-level BSE solver Keywords: X-ray spectroscopy (NBSE).
    [Show full text]
  • "Booklet General Meeting of the GDR REST
    GDR REST General Meeting The GDR-REST aims to bring together different communities of theoretical spectroscopy which are/were historically separated, but unified under a very precise and important subject: the excited-states spectroscopy of variety of systems (for both weakly and strongly correlated systems, for valence and core electrons, etc.). One of the objectives is also to extend the collaboration to the nuclear physics community which might use very similar approaches based on Green's functions. Retracing the GDR-REST footsteps, the Roscoff meeting will be of an interdisciplinary nature, in order to establish the state-of-the-art approaches, share knowledge, identify important issues and unresolved problems, and indicate future directions for the different communities. For this reason four main lectures have been scheduled aiming to introduce the participants to the core electrons spectroscopy, to create a connection with nuclear physics and chemistry communities and to activate discussion on new mathematical developments and algorithms. The meeting will take place at the Biological Station in Roscoff (SBR http://www.sb-roscoff.fr/), Roscoff Marine Station Research and training in marine biology, created in 1872 and affiliated to the CNRS and the University Pierre and Marie Curie. This station, situated on the north coast of Brittany, hosts a CNRS conference centre and is located in Place Georges Teissier, 29680 Roscoff. All meals (and the poster session) will be served at the Gulf Stream restaurant, located at 800m from the Conference Centre. The accommodation of participants will take place both at the Gulf Stream and at the Hotel de France (located by the Conference Centre).
    [Show full text]
  • S.A. Raja Pharmacy College Vadakkangulam-627 116
    S.A. RAJA PHARMACY COLLEGE VADAKKANGULAM-627 116 MEDICINAL CHEMISTRY -III VI SEMESTER B. PHARM PRACTICAL MANUAL CONTENT S.No Experiment Name Page No. 1. Synthesis of Sulphanilamide 01 2. Synthesis of 7- Hydroxy -4- methyl coumarin 03 3. Synthesis of Chlorbutanol 05 4. Synthesis of Tolbutamide 07 5. Synthesis of Hexamine 09 6. Assay of Isonicotinic acid hydrazide 11 7. Assay of Metronidazole 13 8. Assay of Dapsone 16 9. Assay of Chlorpheniramine Maleate 18 10. Assay of Benzyl Penicillin 20 11. Synthesis of Phenytoin from Benzil by Microwave 23 Irradiation 12. Synthesis of Aspirin Assisted by Microwave Oven 26 13. Drawing structure and Reaction using Chemsketch 28 MEDICINAL CHEMISTRY- III Experiment No: 01 Synthesis of Sulphanilamide Aim: To synthesis and submit sulphanilamide from p-acetamido benzene sulphanilamide and calculate its percentage yield. Principle: Sulphanilamide can be prepared by the reaction of P-acetamido benzene sulphanilamide with Hydrochloric acid or ammonium carbonate. The acetamido groups are easily undergo acid catalysed hydrolysis reaction to form p-amino benzene sulphonamide. Reaction: O HN H2N HCl O S O O S O NH NH2 2 4 Acetamidobenzene sulphonamide p Amino benzene sulphonamide Chemical Required: Resorcinol - 1.2 g Ethyl acetoacetate - 2.4 ml Conc. Sulphuric acid - 7.5 ml Procedure: 1.5 gm of 4- acetamido benzene sulphonamide is treated with a mixture of 1 ml of conc. Sulphuric acid diluted with 2 ml water. This mixture is gently heated under reflux for 1 hour. Then 3ml of water is added and the solution is boiled again, with the addition of a small quantity of activated charcoal.
    [Show full text]
  • Interdisciplinary Views on Quantum Many-Body Theory
    23rd ETSF Workshop on Electronic Excitations Interdisciplinary Views on Quantum Many-Body Theory Milan, Italy 10 – 14 September 2018 Welcome The bi-annual workshop of the European Theoretical Spectroscopy Facility (ETSF) provides a forum for excited states and spectroscopy in condensed matter physics, chemistry, nanoscience, materials science, and molecular physics, attracting theoreticians, code developers, and exper- imentalists alike. The 2018 edition aims at fostering the cross-fertilization between different approaches to many- body phenomena, transcending the traditional barriers between disciplines. The workshop will therefore bring together experts facing similar problems from different perspectives, for different applications, and often with a different language. Besides discussing application of many-body theories to excitations in condensed matter, i.e. the traditional field of expertise of ETSF, topics covered by the workshop will include nuclear physics, quantum chemistry, ul- trafast excitation dynamics, quantum transport, topological insulators and novel algorithmic approaches to many-body problems inspired by machine learning and data science. Workshop topics include: quantum chemistry • nuclear physics • machine learning / data science • ultrafast excitation dynamics • topological insulators • quantum transport • We are glad to welcome you in Milan and wish you an inspiring workshop with lots of interesting science and fruitful discussions. The organizers 3 General information General information Organizing and program
    [Show full text]
  • Proton Disorder in Cubic Ice: Effect on the Electronic and Optical Properties
    Zurich Open Repository and Archive University of Zurich Main Library Strickhofstrasse 39 CH-8057 Zurich www.zora.uzh.ch Year: 2015 Proton disorder in cubic ice: effect on the electronic and optical properties Garbuio, Viviana ; Cascella, Michele ; Kupchak, Igor ; Pulci, Olivia ; Seitsonen, Ari Paavo Abstract: The proton disorder in ice has a key role in several properties such as the growth mode, ther- modynamical properties, and ferroelectricity. While structural phase transitions from proton disordered to proton ordered ices have been extensively studied, much less is known about their electronic and optical properties. Here, we present ab initio many body perturbation theory-based calculations of the electronic and optical properties of cubic ice at different levels of proton disorder. We compare our results with those from liquid water, that acts as an example of a fully (proton- and oxygen-)disordered system. We find that by increasing the proton disorder, a shrinking of the electronic gap occurs inice,andit is smallest in the liquid water. Simultaneously, the excitonic binding energy decreases, so that the final optical gaps result to be almost independent on the degree of proton disorder. We explain these findings as an interplay between the local dipolar disorder and the electronic correlation. DOI: https://doi.org/10.1063/1.4929468 Posted at the Zurich Open Repository and Archive, University of Zurich ZORA URL: https://doi.org/10.5167/uzh-114303 Journal Article Published Version Originally published at: Garbuio, Viviana; Cascella, Michele; Kupchak, Igor; Pulci, Olivia; Seitsonen, Ari Paavo (2015). Proton disorder in cubic ice: effect on the electronic and optical properties.
    [Show full text]
  • Efficient Theoretical and Numerical Approaches Towards a Dynamical Many-Body Theory
    Damping, satellites and multiple excitations in oxides and nanostructures: efficient theoretical and numerical approaches towards a dynamical many-body theory Lorenzo Sponza To cite this version: Lorenzo Sponza. Damping, satellites and multiple excitations in oxides and nanostructures: efficient theoretical and numerical approaches towards a dynamical many-body theory. Materials Science [cond-mat.mtrl-sci]. Ecole Polytechnique (EDX), 2013. English. tel-01883527 HAL Id: tel-01883527 https://hal.archives-ouvertes.fr/tel-01883527 Submitted on 15 Oct 2018 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Thèse présentée pour obtenir le grade de DOCTEUR DE L’ÉCOLE POLYTECHNIQUE par LORENZO SPONZA Damping, satellites and multiple excitations in oxides and nanostructures: efficient theoretical and numerical approaches towards a dynamical many-body theory Thèse soutenue le 30 Octobre 2013 Silke BIERMANN Président Angel RUBIO Rapporteur Valerio OLEVANO Rapporteur Odile STÉPHAN Examinatrice Mark VAN SCHILFGAARDE Examinateur Christine GIORGETTI Co-directrice Lucia REINING Directrice Table of Contents 1 Introduction 1 1.1 An introduction to spectroscopy . .2 1.2 Many-body interactions and dynamical effects . .3 1.3 Dynamical effects in real systems . .4 1.3.1 Photoemission and plasmon satellites .
    [Show full text]
  • Ab Initio High-Energy Excitonic Effects in Graphite and Graphene
    RAPID COMMUNICATIONS PHYSICAL REVIEW B 81, 121405͑R͒͑2010͒ Ab initio high-energy excitonic effects in graphite and graphene Paolo E. Trevisanutto,1,2,3 Markus Holzmann,4,5,3 Michel Côté,2 and Valerio Olevano1,3 1Institut Néel, CNRS and UJF, Grenoble, France 2Départment de Physique and RQMP, Université de Montréal, Quebéc, Canada 3European Theoretical Spectroscopy Facility (ETSF), France 4LPMMC, CNRS and UJF, Grenoble, France 5LPTMC, CNRS and UPMC, Paris, France ͑Received 9 September 2009; revised manuscript received 3 February 2010; published 4 March 2010͒ We present ab initio many-body calculations of the optical absorption in bulk graphite, graphene and bilayer of graphene. Electron-hole interaction is included solving the Bethe-Salpeter equation on top of a GW quasi- particle electronic structure. For all three systems, we observe strong excitonic effects at high energy, well transitions. In ءtransitions. In graphite, these affect the onset of ␴→␴ ءbeyond the continuum of ␲→␲ graphene, we predict an excitonic resonance at 8.3 eV arising from a background continuum of dipole forbid- den transitions. In the graphene bilayer, the resonance is shifted to 9.6 eV. Our results for graphite are in good agreement with experiments. DOI: 10.1103/PhysRevB.81.121405 PACS number͑s͒: 78.20.Bh, 71.35.Cc, 78.40.Ϫq structure and reshape it. Both, in the perpendicular ءGraphene, a recently discovered two-dimensional ͑2D͒ the ␴-␴ hexagonal crystal carbon sheet,1 has attracted much interest and in the parallel polarization, our spectra are in very good due to its exotic electronic properties. The comparison with agreement with experiment, in particular with Ref.
    [Show full text]
  • Arxiv:1601.07728V1
    Efficient implementation of core-excitation Bethe-Salpeter equation calculations K. Gilmorea,b,∗, John Vinsonc, E.L. Shirleyc, D. Prendergastd, C.D. Pemmarajud, J.J. Kase, F.D. Vilae, J.J. Rehre aEuropean Synchrotron Radiation Facility (ESRF), Grenoble 38000, France bJiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft Materials (FUNSOM), Soochow University, Suzhou, Jiangsu 215123, PR China cNational Institute of Standards and Technology (NIST), Gaithersburg, Maryland 20899, USA dLawrence Berkeley National Lab (LBL), Berkeley, California 94720, USA eDepartment of Physics, University of Washington, Seattle, Washington 98195, USA Abstract We present an efficient implementation of the Bethe-Salpeter equation (BSE) method for obtaining core-level spectra including x-ray absorption (XAS), x-ray emission (XES), and both resonant and non-resonant inelastic x-ray scattering spectra (N/RIXS). Calculations are based on density functional theory (DFT) electronic structures generated either by abinit or Quantumespresso, both plane-wave basis, pseudopotential codes. This electronic structure is improved through the inclusion of a GW self energy. The projector augmented wave technique is used to evaluate transition matrix elements between core-level and band states. Final two-particle scattering states are obtained with the NIST core-level BSE solver (NBSE). We have previously reported this implementation, which we refer to as ocean (Obtaining Core Excitations from Ab initio electronic structure and NBSE) [Phys. Rev. B 83, 115106 (2011)]. Here, we present additional efficiencies that enable us to evaluate spectra for systems ten times larger than previously possible; containing up to a few thousand electrons. These improvements include the implementation of optimal basis functions that reduce the cost of the initial DFT calculations, more complete parallelization of the screening calculation and of the action of the BSE Hamiltonian, and various memory reductions.
    [Show full text]
  • Electronic and Optical Properties of Silicon Nanocrystals
    Electronic and Optical Properties of Silicon Nanocrystals Ceyhun Bulutay1 and Stefano Ossicini2 1Department of Physics, Bilkent University, Bilkent, Ankara 06800, Turkey 2CNR-INFM-S3 and Dipartimento di Scienze e Metodi dell’Ingegneria, Universit`adi Modena e Reggio Emilia, via Amendola 2 Pad. Morselli, I-42100 Reggio Emilia, Italy. The previous decades repeatedly witnessed claims that silicon would be sidelined by various alternative material systems. In the long run, none of these claims turned out to be the case. Taking into account the changing societal and technological needs, there are strong indications that the nanocrystalline form of silicon will provide a critical support to sustain this domination as the all-purpose material of choice. The purpose of this study is to offer a comprehensive theoretical overview of the electronic structure and optical properties of Si nanocrystals (Si NCs). Starting with small NCs, we use a first-principles methodology taking into account the structural relaxations. We go beyond the one-particle approach including the self-energy corrections, by means of the GW approximation, and the excitonic effects, through the solution of the Bethe-Salpeter equation. This new approach, where many-body effects are combined with a study of the structural distortion due to the impurity atoms in the excited state, allows to calculate accurately the Stokes shift between absorption and photoluminescence spectra. Regarding the interface and impurity effects, first, the hydrogenated Si NCs are considered, followed by the discussion of oxidation, and of (co-)doping and finally, of the crystalline as well as amorphous embedding matrix. For the larger Si NCs embedded in a wide band-gap matrix containing of the order of 10,000’s of atoms, an atomistic semi-empirical pseudopotential approach is utilized.
    [Show full text]