Computational Screening of Chalcogen-Terminated Inherent Multilayer MXenes and MAX Precursors.

Sulfur-terminated single sheet (ss-)MXene was recently achieved by delamination of multilayered van der Waals bonded (vdW)-MXenes NbCS and TaCS synthesized through solid-state synthesis, rather than via the traditional way of selectively etching A-layers from the corresponding MAX phase. Inspired by this, we perform a computational screening study of vdW-MXenes MCCh isotypical to NbCS and TaCS, with M = Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Mo, or W and Ch = S, Se, or Te. The thermodynamic stability of each vdW-MXene MCCh is assessed, and the dynamical stability of both vdW- and ss-MXene is considered through phonon dispersions. We predict seven stable vdW-MXenes, out of which four have not been reported previously, and one, VCSe, incorporates a new transition metal element into this family of materials. Electronic properties are presented for the vdW- and ss-forms of the stable vdW-MXenes, suggesting that the materials are either metallic, semimetallic, or semiconducting. In previous experimental reports the vdW-MXene NbCS is synthesized by manipulation of the corresponding MAX phase NbSC. Therefore, we also evaluate the thermodynamic stability of the corresponding MAX phases, identifying 15 potentially stable phases. Six of these are experimentally reported, leaving nine new MAX phases for future experimental investigation.