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Title: Optical properties of alkali halide crystals from all-electron hybrid TD-DFT calculations

We present a study of the electronic and optical properties of a series of alkali halide crystals AX, with A = Li, Na, K, Rb and X = F, Cl, Br based on a recent implementation of hybrid-exchange time-dependent density functional theory (TD-DFT) (TD-B3LYP) in the all-electron Gaussian basis set code CRYSTAL. We examine, in particular, the impact of basis set size and quality on the prediction of the optical gap and exciton binding energy. The formation of bound excitons by photoexcitation is observed in all the studied systems and this is shown to be correlated to specific features of the Hartree-Fock exchange component of the TD-DFT response kernel. All computed optical gaps and exciton binding energies are however markedly below estimated experimental and, where available, 2-particle Green’s function (GW-Bethe-Salpeter equation, GW-BSE) values. We attribute this reduced exciton binding to the incorrect asymptotics of the B3LYP exchange correlation ground state functional and of the TD-B3LYP response kernel, which lead to a large underestimation of the Coulomb interaction between the excited electron and hole wavefunctions. Considering LiF as an example, we correlate the asymptotic behaviour of the TD-B3LYP kernel to the fraction of Fock exchange admixed in the ground state functionalmore » c{sub HF} and show that there exists one value of c{sub HF} (∼0.32) that reproduces at least semi-quantitatively the optical gap of this material.« less
Authors:
;  [1] ;  [2]
  1. Thomas Young Centre, Department of Chemistry, Imperial College London, South Kensington, London SW7 2AZ (United Kingdom)
  2. Rutherford Appleton Laboratory, STFC, Harwell Oxford, Didcot OX11 0QX (United Kingdom)
Publication Date:
OSTI Identifier:
22415949
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 142; Journal Issue: 21; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ASYMPTOTIC SOLUTIONS; BETHE-SALPETER EQUATION; BINDING ENERGY; CORRELATIONS; CRYSTALS; DENSITY FUNCTIONAL METHOD; ELECTRONS; EXCITONS; GROUND STATES; HARTREE-FOCK METHOD; HOLES; KERNELS; LITHIUM FLUORIDES; OPTICAL PROPERTIES; PARTICLES; RUBIDIUM BROMIDES; TIME DEPENDENCE; WAVE FUNCTIONS