Electronic structure and optical properties of lightweight metal hydrides

Abstract

, using first-principles densityfunctional theory and GW calculations. All compounds are large gap insulators with GW single-particle band gaps varying from 3.5 eV in AlH 3 to 6.6 eV in LiAlH 4 . Despite considerable differences between the band structures and the band gaps of the various compounds, their optical responses are qualitatively similar. In most of the spectra the optical absorption rises sharply above 6 eV and has a strong peak around 8 eV. The quantitative differences in the optical spectra are interpreted in terms of the structure and the electronic structure of the compounds. In the simple hydrides the valence bands are dominated by the hydrogen atoms, whereas the conduction bands have mixed contributions from the hydrogens and the metal cations. The electronic structure of the aluminium compounds is determined mainly by aluminium hydride complexes and their mutual interactions.

LiH as a Li+ and H− ion provider

“…The calculated formation enthalpy of LiH at 0 K is −0.825 eV (or −0.879 eV in HSE06); for comparison, the experimental value at 300 K is −0.94 eV [32]. Our GGA results for the bulk properties are in good agreement with those reported by other groups [33,34].…”

First-principles study of the optical properties ofMgxTi1−xH2

“…The parent compound ␣-MgH 2 is an insulator with a band gap close to 6 eV. 9,42 The band gap of the cubic phase ␤-MgH 2 is smaller by ϳ1 eV, 17 which means that it is still a large band-gap material without absorption in the visible range. As discussed in Sec.…”

“…[1][2][3][4][5][6] The metals are reflective, but after hydrogenation become insulators, and hence in most cases transparent. [7][8][9][10] Especially if an alloy with high hydrogen mobility is used and applied in thin films, the optical switching can be fast, reversible, and robust. 11 Recently, metastable thin films composed of various composition ratios of magnesium and titanium have been shown to exhibit remarkable optical properties which could be especially useful for smart solar cell coatings and hydrogen sensor applications.…”

“…The calculated densities of states show a predominant hydrogen-s character below the Fermi level, which is typical for metal hydrides, where electrons are transferred to the hydrogen atoms. 9,10,26 However, unlike the closed-shell hydrides, in Mg x Ti 1−x H 2 a considerable density of states ͑DOS͒ is found at the Fermi level, which is mainly composed of titanium-d states. This suggests a metallic response and one might naively expect Mg x Ti 1−x H 2 to be reflective instead of black.…”

Classification of hydrides according to features of band structure

“…Structural and positional parameters used in the present calculations for the hydrides have been obtained from Refs. [4,10,[21][22][23][24][25][26].…”