Computational studies on the structural, electronic, and optical properties of Ti2CO2 MXene using the (DFT + U) method

The structural, electronic, and optical properties of the Ti₂CO₂ monolayer were systematically investigated using density functional theory (DFT) with (PBE-GGA + U) corrections. The optimal Hubbard parameters for Ti atoms were 4.72 eV using ultrasoft pseudopotentials (USPP) and 4.51 eV using norm-conserving (NC) pseudopotentials to accurately account for electron-electron interactions. The monolayer exhibits an indirect band gap, increased compared to standard (PBE-GGA) calculations. Partial density of states analysis shows that the valence band is dominated by C-2p and O-2p orbitals, while the conduction band is mainly composed of Ti-3d orbitals, governing optical transitions. The optical response displays strong anisotropy, with absorption onsets at 0.99 eV (E∥X) and 1.44 eV (E∥Z), and plasmonic maxima at 7.72 eV and 7.66 eV. Refractive indices at zero energy are 1.67 and 1.37, confirming anisotropic behavior. Electron-electron interactions shift peak positions and broaden spectral features. These properties make Ti₂CO₂ a promising candidate for photodetectors, solar energy, photocalists, and transparent conductive coatings, providing a theoretical basis for experimental validation and guiding the design of multifunctional 2D MXene-based nanodevices.