Comprehensive Characterization of Alkaline Earth Metal Halides using First Principles Calculations

Alkaline earth metal halides are among the scarce insulators with dielectric constants and band gaps larger than those of SiO₂. Here, we present a study of this class of high K/large band gap materials using first principles calculations with different levels of sophistication. In particular we focus on changes in their electronic and thermal properties as a function of composition and structure. Our results show that the most stable phases of these materials are those with larger band gaps. Determination of their band gaps requires hybrid approaches to overcome well-known limitations of density functional theory. Phonon properties and dielectric response are compared using different exchange-correlation functionals: (i) Localized Density Approximation (LDA), (ii) Generalized Gradient Approximation (GGA) and (iii) Generalized Gradient Approximation including van der Waals forces (GGA+vdW). We find that the dispersive forces correct the mode softening observed in low-frequency phonon modes in the GGA functionals yielding results similar to LDA. The different trends found in these materials class relative to their composition and structure are discussed.