First-Principles Calculation of MoO 2 and MoO 3 Electronic and Optical Properties Compared with Experimental Data.

MoO 3 and MoO 2 systems have attracted particular attention for many widespread applications thanks to their electronic and optical peculiarities; from the crystallographic point of view, MoO 3 adopts a thermodynamically stable orthorhombic phase (α-MoO 3 ) belonging to the space group Pbmn , while MoO 2 assumes a monoclinic arrangement characterized by space group P 2 1 / c. In the present paper, we investigated the electronic and optical properties of both MoO 3 and MoO 2 by using Density Functional Theory calculations, in particular, the Meta Generalized Gradient Approximation (MGGA) SCAN functional together with the PseudoDojo pseudopotential, which were used for the first time to obtain a deeper insight into the nature of different Mo-O bonds in these materials. The calculated density of states, the band gap, and the band structure were confirmed and validated by comparison with already available experimental results, while the optical properties were validated by recording optical spectra. Furthermore, the calculated band-gap energy value for the orthorhombic MoO 3 showed the best match to the experimental value reported in the literature. All these findings suggest that the newly proposed theoretical techniques reproduce the experimental evidence of both MoO 2 and MoO 3 systems with high accuracy.