First-Principles Study of the Structural, Optical, Dynamical and Thermodynamic Properties of BaZn $$\hbox {O}_{2}$$ O 2 Under Pressure

Abstract

The structural, optical, dynamical, and thermodynamic properties of BaZn\(\hbox {O}_{2}\) under pressure are studied based on the density functional theory. The calculated structural parameters are consistent with the available experimental data. In the ground state, the electronic band structure and density of states indicate that BaZn\(\hbox {O}_{2}\) is an insulator with a direct gap of 2.2 eV. The Mulliken charges are also analyzed to characterize the bonding property. After the structural relaxation, the optical properties are studied. It is found that the dielectric function of E\(\Vert x\hbox { and }E\Vert y\) are isotropic, whereas the \(E\Vert x\) and \(E\Vert z\) are anisotropic. The effect of pressure on the energy-loss function in the ultraviolet region becomes more obvious as the pressure increases. Furthermore, the dynamical properties under different pressures are investigated using the finite displacement method. We find that the \(P3_{1}21\) phase of \(\hbox {BaZn}\hbox {O}_{2}\) is dynamically stable under the pressure ranging from 0 GPa to 30 GPa. The phonon dispersion curves, phonon density of states, vibrational modes and atoms that contribute to these vibrations at \({{\varvec{\Gamma }}}\) point under different pressures are also reported in this work. Finally, by employing the quasi-harmonic approximation, the thermodynamic properties such as the temperature dependence of the thermal expansion coefficient, specific heat, entropy and Gibbs free energy under different pressures are investigated. It is found that the influences of the temperature on the heat capacity are much more significant than that of the pressure on it.