Electronic structure and optical properties of magnesium tetraborate: An ab initio study

The structural, electronic and optical properties of important dosimeter material MgB4O7 have been analyzed on the basis of the first-principles density functional theory calculations. Optimizations of the crystal structure have been performed using the standard local density approximation for the exchange correlation (XC) functional whereas the electronic structure and linear optical properties were calculated using the semi-local XC potential of Tran and Blaha. The calculated lattice constants and atomic positions are found to be in good agreement with the experimental values. The calculated band gap is found to be direct (Gamma -> Gamma), with the value of 9.58 eV, consistent with the values which were determined or estimated for similar compounds. The top of the valence band is dominated by the O 2p-states, while the conduction band bottom consists predominantly of the 2p-states of the B ions with trigonal coordination with neighboring O's. Optical absorption spectrum is characterized by two prominent peaks. The lower energy peak originates from electron transitions within the trigonal B-O structural groups, while the higher energy peak is determined by electron transitions within the tetrahedral B-O groups and polyhedral Mg-O structural motifs. All calculated optical properties are found to be anisotropic. (C) 2016 Elsevier B.V. All rights reserved.