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 ZrnCn-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 F 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 (ZrnCn-1)O-2, Zr2CO2 is a semiconductor, Zr3C2O2 is a semimetal, and Zr4C3O2 becomes a metal.