A First-Principles Study on the Vibrational and Electronic Properties of Zr-C MXenes

Within the framework of density functional theory calculations, the structural, vibrational, and electronic properties of Zr_nC_n-1 (n=2, 3, and 4) and their functionalized MXenes have been investigated. We find that the most stable configurations for Zr-C MXene are the ones that the terminal groups F, O, and OH locate on the common hollow site of the superficial Zr layer and its adjacent C layer. F and OH-terminated Zr₃C₂ and Zr₄C₃ have small imaginary acoustic phonon branches around Γ point while the others have no negative phonon modes. The pristine MXenes (Zr₂C, Zr₃C₂ and Zr₄C₃) are all metallic with large DOS contributed by the Zr atom at the Fermi energy. When functionalized by F, O and OH, new hybridization states appear and the DOS at the Fermi level are reduced. Moreover, we find that their metallic characteristic increases with an increase in n. For (Zr_nC_n-1)O₂, Zr₂CO₂ is a semiconductor, Zr₃C₂O₂ is a semimetal, and Zr₄C₃O₂ becomes a metal.