Theoretical investigations on the elastic, electronic and thermal properties of orthorhombic Li2CdGeS4 under pressure

The structural, elastic, electronic, optical and thermal properties of orthorhombic Li2CdGeS4 have been performed by the first-principles plane-wave pseudopotential method. The calculated structural parameters and elastic constants at zero pressure and temperature are in good agreement with the available theoretical result. The dependence of the elastic constants C-ij, the aggregate elastic modulus B, G and the anisotropies of Li2CdGeS4 under pressure have been investigated. By the elastic stability criteria, it is predicted that orthorhombic Li2CdGeS4 is not stable above 8.6 GPa. The electronic band structures and optical properties of Li2CdGeS4 under pressure are studied. It is found that a direct band gap at zero pressure induced by the G-G transition is presented, which is 2.421 eV (LDA). Moreover, the direct energy band gap (G-G) transforms to the indirect energy gap (along G-X point) at about 4 GPa. The refractive and the absorption indexes under pressure suggest that the strong absorption spectrum appears mostly in the ultra-violet region, and the optical absorption decreases with photon energy in the high energy range. Finally, by using a quasi-harmonic Debye model, the heat capacity and Gruneisen parameter are also obtained successfully. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.