Optical band gap of 3 from first-principles calculations.

Although there are intensive studies on technetium oxide 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 (), the exchange constant and the Néel temperature are investigated. The inter-site exchange constant between antiferromagnetic 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 with the experimental value. It is found that when U = 2.3 eV, J = 0.3 eV are included for 4d in GGA + U calculations, the local magnetic moment of in orthorhombic 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. [ABSTRACT FROM AUTHOR]