Comparative first-principles calculations of electronic, optical and elastic anisotropy properties of Cs XBr 3 ( X=Ca,Ge,Sn ) crystals
Detailed ab initio calculations of the structural, electronic, optical and elastic properties of CsCaBr 3, CsGeBr 3 and CsSnBr 3 crystals are presented in this paper. Based on the obtained results, CsCaBr 3 is characterized as a dielectric with an indirect band gap, whereas CsGeBr 3 and CsSnBr 3 are semiconductors with very narrow direct band gaps. The first theoretical estimations of the refractive indexes for all compounds are reported. Variations of the electron density difference distribution induced by changes of the second cation were analyzed and related to the type of chemical bonding between atoms. In addition, the complete set of elastic parameters (which includes the elastic constants, elastic compliance constants, bulk and Young's moduli, elastic anisotropy) was obtained. Directional anisotropy of elastic properties was visualized; the directions in the crystal lattices, along which the maximal and minimal values of the Young's moduli are realized, were identified.