First Principles Calculation of Band Structure and Physical Properties of Ferroelectric (NH4)2BeF4 Crystal

Abstract

Ab initio calculations of the ferroelectric phase ammonium fluoroberyllate crystal (NH4)2BeF4(AFB) (space group $\boldsymbol{Pcn2}_{1})$ in the framework of density functional theory (DFT) were conducted for the first time. Information about position of electronic levels and energy bands was obtained. It was revealed, that ferroelectric AFB has direct energy gap with a bandgap value $\boldsymbol{E}_{g}=6.79\mathbf{eV}$. Frequency-dependent dielectric functions $\varepsilon(\omega)$ were calculated and analyzed.