DFT+U Optical Features of Thermochromic \(\text {VO}_{2}\) : A Powerful Tool Towards Functional Daytime Radiative Passive Cooling Implementation

The structural, electronic and optical properties of both monoclinic and rutile polymorphs of vanadium dioxide, \(\text {VO}_{2}\) , have been determined by means of first-principles calculations based on semiempirical DFT+U method. The outcome shows that the Hubbard U scheme provides bandgap values consistent with previously reported experimental ones. The simulated optical properties for the high-temperature rutile polymorph correctly reproduce the metallic behaviour of the system. It is interesting to note that at low temperatures, the \(\text {VO}_{2}\) monoclinic structure is more transparent under infrared light irradiation, while the rutile phase blocks the same IR light, as demonstrated by the simulated optical reflectance and absorption coefficient. This work aims to provide the readers with a comprehensive understanding of the complex chemistry of \(\text {VO}_{2}\) , paving the way to future studies addressing the doping effect on the optical and thermal behaviour of the system in view of the application of such material in devices for radiative cooling.