Based on ab initio calculations and metadynamics simulations, we predict that the electronic gap of $2H$-MoS${}_2$, a layered insulator, will close under pressures in excess of 25 to 35 GPa. In the same pressure range, simulations and enthalpy optimization predict a structural transition. Free mutual sliding of layers takes place at this transition, the original $2H_c$ stacking changing to a $2H_a$ stacking typical of $2H$-NbSe${}_2$, an event explaining for the first time previously mysterious x-ray diffraction and Raman data. Phonon and electron phonon calculations suggest that pristine MoS${}_2$ will remain semimetallic up to very high pressures and is thus unlikely to develop superconductivity as it does upon metal intercalation.

• Received 7 November 2012

DOI:https://doi.org/10.1103/PhysRevB.87.144105