Structural, electronic, and optical properties of (2D)MXenes Zr₂CT₂(T = O and F) studied using the (DFT + U) method.

In this study, we investigate the effects of electron-electron interactions on the structural, electronic, and optical properties of the (2D)MXenes Zr₂CO₂ and Zr₂CF₂. The objective is to enhance the understanding of these interactions and their impact on the electronic and optical characteristics of these monolayers, which have significant potential for various nanotechnology applications. Using the Quantum ESPRESSO package and advanced computational methods including density functional theory (DFT), the generalized gradient approximation (GGA), and the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional, the optimal Hubbard U parameters for Zr atoms in the semiconductor Zr₂CO₂ and the metallic Zr₂CF₂ MXenes were determined. For ultrasoft Pseudopotentials (USPP), these values were calculated to be 2.889 eV and 3.2680 eV, respectively, while for the harder Martins-Troullier (MT) Pseudopotentials, they were 3.174 eV and 3.840 eV, respectively. Subsequently, we analyzed the band structures and the electronic and optical properties characteristics of these MXenes. By accounting for electron-electron interactions for the Zr₂CO₂ semiconductor monolayer, the indirect bandgap increased by 0.311 eV and 0.276 eV when using (USPP) and (MT) Pseudopotentials, respectively. Additionally, high optical absorption coefficients were observed in the visible and ultraviolet regions. In contrast, the bandgap in the metallic Zr₂CF₂ monolayer shifted from a negative value toward zero, resulting in values of 0.085 eV and 0.031 eV for (USPP) and (MT) Pseudopotentials, respectively. MXene Zr₂CF₂ emerges as a promising candidate for absorption and conductivity in the infrared region, which is vital for various applications. These findings provide a deeper understanding of the electronic and optical behavior of the Zr₂CO₂ and Zr₂CF₂ (2D) monolayers and pave the way for developing novel applications in electronic and optical technologies.