High-pressure structural, lattice dynamics, and electronic properties of beryllium aluminate studied from first-principles theory

The present work reports the complete study of structural, vibrational, mechanical, and electronic properties of BeAl2O4 (known as Chrysoberyl) using first-principles computing methods. The calculated ground-state properties agree quite well with previous experiments. The computed phonon dispersion curves do not show imaginary frequencies confirming the dynamical stability. In addition, the calculated elastic constants also ensure the mechanical stability through fulfillment of mechanical stability criteria. Apart from that, the theoretically determined phonon frequencies agree quite well with previous Raman and infrared experiments at ambient conditions. Various thermodynamic properties are also being calculated as a function of temperature. The thermal expansion computed within the quasi-harmonic approximation is found to be positive in agreement with the experiments. From the electronic structure we can see that Chrysoberyl possess a direct band gap of 8.3 eV with the oxygen- 2p states dominating close to fermi level in the valence band. The influence of pressure on different properties is discussed. The highlight of the present work is the presence of optical isotropy in Chrysoberyl although the crystal structure is highly anisotropic