Hybrid density functional study of structural and electronic properties of functionalized Ti n + 1 X n ( X = C , N) monolayers

Density functional theory simulations with conventional (PBE) and hybrid (HSE06) functionals were performed to investigate the structural and electronic properties of MXene monolayers, ${\mathrm{Ti}}_{n+1}{\mathrm{C}}_{n}$ and ${\mathrm{Ti}}_{n+1}{\mathrm{N}}_{n}$ ($n=1$--9) with surfaces terminated by O, F, H, and OH groups. We find that PBE and HSE06 give similar results. Without functional groups, MXenes have magnetically ordered ground states. All the studied materials are metallic except for ${\mathrm{Ti}}_{2}{\mathrm{CO}}_{2}$, which we predict to be semiconducting. The calculated density of states at the Fermi level of the thicker MXenes ($n\ensuremath{\geqslant}5$) is much higher than for thin MXenes,…