Optical band gap of SrTcO3 from first-principles calculations

Abstract

Although there are intensive studies on technetium oxide SrTcO 3 recently, its ground-state band structure has never been given and no consensus on its band gap is obtained. We use the generalized gradient approximation (GGA) with on-site Coulomb corrections (GGA + U) method to study its band structure and the optical band gap. A series of on-site interaction U and J values are employed in the calculations and the concomitant evolutions of the electronic structure, local magnetic moment of technetium ( Tc ), the exchange constant and the Néel temperature are investigated. The inter-site exchange constant between antiferromagnetic Tc atoms through medium oxygen is found to increase firstly and then decrease with an increasing U, in agreement with the trend obtained by tight-binding method. The appropriate on-site U and J values are calibrated by comparing the calculated local magnetic moment of Tc with the experimental value. It is found that when U = 2.3 eV, J = 0.3 eV are included for Tc 4d in GGA + U calculations, the local magnetic moment of Tc in orthorhombic SrTcO 3 is 2.01 μB, the same as the experimental value obtained at 4 K. The calculated band structure shows that the band gap is a direct band gap with a magnitude of 1.61 eV.