DFT and DFT+U Insights into the Physical Properties of UO₂

Abstract

This study reports the structural, electronic, magnetic, elastic, thermal, and optical properties of UO₂ solid crystalline material by applying DFT and DFT+U approximation methods. The direct band gap Mott-Insulating electronic properties are found successfully by using both the LDA+U and GGA+U functionals, and the energy band gap values are obtained in the range from 1.725 to 2.860 eV. The XRD and Neutron diffraction peaks confirmed the fcc-structured fluorite type UO₂. UO₂ is found mechanically stable and ductile from elastic constants calculations. The lattice thermal conductivity is 8.8 Wm^-1 K^-1 at 323 K, which is very close to the reported theoretical and experimental results. The frequency-dependent optical parameters are calculated from complex dielectric functions, which indicate that UO₂ is simultaneously an efficient absorber and reflector for ultraviolet radiation in particular energy regions. Although UO₂ is a potential fuel material and cannot be used for conventional optical devices, the anisotropic optical properties, higher dielectric constant, and semiconducting electronic property indicate that the radioactive UO₂ exhibits interesting optoelectronic behaviors also.