Modeling of Hypothetical BeXAs2 (X = Si, Ge, Sn) Crystal Structure and Phonon Spectra

The paper presents ab initio density functional calculations of the geometry optimization of BeXAs2 (X = Si, Ge, Sn) crystal structure, primitive cells and phonon spectra in the centre of the Brillouin zone. Interpolation of phonon spectra was performed over the Brillouin zone using the Keating model. Ab initio frequency calculations are used to ascertain the Keating parameters via program optimization. The values of phenomenological parameters are in good agreement with the parameters of the chemical bond obtained by ab initio calculations. The partial phonon spectra are investigated. The structure of acoustic and optical branches of the full phonon spectrum is determined mostly by the ion mass ratio of the crystal compounds.