Optical response of the sodium alanate system: GW0-BSE calculations and thin film measurements

Journal article (2011)

Authors

MJ van Setten Radboud Universiteit Nijmegen, Karlsruhe Institut für Technologie
R Gremaud Vrije Universiteit Amsterdam, Swiss Federal Laboratories for Materials Science and Technology (Empa)
G Brocks University of Twente
B. Dam ChemE/Materials for Energy Conversion and Storage - AS , Vrije Universiteit Amsterdam
G Kresse University of Vienna
GA de Wijs Radboud Universiteit Nijmegen
Research Group
ChemE/Materials for Energy Conversion and Storage (AS) (TU Delft)
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Published Date

2011

Language

English

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Faculty

Applied Sciences

Department

ChemE/Chemical Engineering

Research Group

ChemE/Materials for Energy Conversion and Storage

Abstract

We calculate from first principles the optical spectra of the hydrides in the sodium alanate hydrogen storage system: NaH, NaAlH4, and Na 3AlH6. In particular we study the effects of systematic improvements of the theoretical description. To benchmark the calculations we also measure the optical response of a thin film of NaH. The simplest calculated dielectric functions are based upon independent electrons and holes, whose spectrum is obtained at the G0W0 level. Successive improvements consist of including partial self-consistency (so-called GW 0) and account for excitonic effects, using the Bethe-Salpeter equation (BSE). Each improvement gives a sizable blue shift or red shift of the dielectric functions, but conserves the trend in the optical gap among different materials. Whereas these shifts partially cancel at the highest (GW 0-BSE) level of approximation, the shape of the dielectric functions is strongly modified by excitonic effects. Calculations at the GW 0-BSE level give a good agreement with the dielectric function of NaH extracted from the measurements. It demonstrates that the approach can be used for a quantitative interpretation of spectra in novel hydrogen storage materials obtained via, e.g., hydrogenography.