First-principles calculation of the electronic and optical properties of Gd2FeCrO6 double perovskite: Effect of Hubbard U parameter

We have synthesized Gd2FeCrO6 (GFCO) double perovskite which crystallized in monoclinic structure with P21/n space group. The UV–visible and photoluminescence spectroscopic analyses confirmed its direct band gap semiconducting nature. Here, by employing experimentally obtained structural parameters in first-principles calculation, we have reported the spin-polarized electronic band structure, charge carrier effective masses, density of states, electronic charge density distribution and optical absorption property of GFCO double perovskite. Moreover, the effects of on-site d–d Coulomb interaction energy (Ueff) on the electronic and optical properties were investigated by applying a range of Hubbard Ueff parameter from 0 to 6 eV to the Fe-3d and Cr-3d orbitals within the generalized gradient approximation (GGA) and GGA + U methods. Notably, when we applied Ueff in the range of 1–5 eV, both the up-spin and down-spin band structures were observed to be direct. The charge carrier effective masses were also found to enhance gradually from Ueff = 1 eV–5 eV, however, these values were anomalous for Ueff = 0 and 6 eV. These results suggest that Ueff should be limited within the range of 1–5 eV to calculate the structural, electronic and optical properties of GFCO double perovskite. Finally we observed that considering Ueff = 3 eV, the theoretically calculated optical band gap ~1.99 eV matched well with the experimentally obtained value ~2.0 eV. The outcomes of our finding imply that the Ueff value of 3 eV most accurately localized the Fe-3d and Cr-3d orbitals of GFCO keeping the effect of self-interaction error from the other orbitals almost negligible. Therefore, we may recommend Ueff = 3 eV for first-principles calculation of the electronic and optical properties of GFCO double perovskite that might have potential in photocatalytic and related solar energy applications