First principle calculation of structural, electronic, optical, elastic and thermodynamic properties of group IIA metal iodides: Structure-property correlation

The Structural, Electronic, Optical, Elastic and Thermodynamic Properties of Group IIA Metal Iodides were investigated using DFT calculations employing full potential linearized augmented plane wave plus local orbitals with Perdew Burke Ernzerhof-Generalized Gradient Approximation (PBE-GGA). We have also carried out band structure calculations using some other exchange-correlation functionals such as LSDA, PBEsol-GGA,WC-GGA and TB-mBJ for all the compounds. Among these iodides, MgI2 and CaI2 have same trigonal structure while SrI2 and BaI2 follow same orthorhombic structure with BeI2 having orthorhombic structure of entirely different space group. All the calculated properties show consistently the similarity for the iodides of same structure following the structure-property correlation. Bands are fewer and less dense for MgI2 and CaI2 in contrast with many and denser bands of SrI2 and BaI2 in comparison to altogether different moderately dense bands of BeI2. The band structure reveals an indirect band gap of 4.08 eV, 3.5 eV, 3.58 eV for BeI2, MgI2, CaI2 respectively and a direct band gap of 3.79, 3.35 for SrI2, BaI2 respectively. The optical anisotropy with excitonic features exhibited by BeI2, MgI2 and CaI2 is clearly absent in SrI2 and BaI2. The calculated elastic constants show that all these compounds are quite mechanically stable having the magnitude of elastic anisotropy in the order: BeI2>CaI2>BaI2>MgI2>SrI2. All the thermodynamic properties show bunching according to their structure consistent with structure-property correlation. Debye temperatures were calculated for BeI2, MgI2, CaI2, SrI2 and BaI2 at room temperature and zero pressure as 183.53 K, 188.51 K, 166.98 K, 151.12 K and 135.55 K respectively. Many parameters of these properties are new in the literature. A reasonable agreement between our calculated and available theoretical/experimental band gaps of these iodides in the literature justifies the accuracy of the calculations of other properties. All the properties of these iodides are explained consistently and comprehensively in terms of their structure-property correlation.