Pressure induced metallization with absence of structural transition in layered MoSe$_{2}$

Layered transition-metal dichalcogenides 2H-MX$_{2}$ (M $=$ Mo, W, and etc, X $=$ S, Se, and Te) are emerging as exciting material systems with unique electronic properties and atomically thin geometries. Here, we systematically investigating the high pressure behavior of 2H$_{\mathrm{c}}$-MoSe$_{2}$ up to 60 GPa via a diamond anvil cell, we identified MoSe$_{2}$ as a promising candidate for lattice and electronic engineering. In sharp contrast to MoS$_{2}$, the crystal structure of MoSe$_{2}$ evolves from an anisotropic two-dimensional layered network to a highly isotropic three-dimensional solid without any structural transition. The role of the chalcogenides anions in stabilizing either 2H$_{\mathrm{a}}$ or 2H$_{\mathrm{c}}$ layered patterns is underscored by our layer sliding calculations. MoSe$_{2}$ possesses highly tunable optical and electrical transport properties as a function of pressure, which is essentially determined by the narrowing of its band gap followed by closure at around 40 GPa. Our ab-initio calculations further support the semiconductor to metal transition.