Bonding Charge Density and Ultimate Strength of Monolayer Transition Metal Dichalcogenides

We have carried out first-principles density functional calculations on the mechanical response of two-dimensional (2D) monolayer group VI transition metal dichalcogenides (TMDs) to large elastic deformation. We find that the ultimate strength and the overall stress response of these 2D materials is strongly influenced by their chemical composition and loading direction. We demonstrate that differences in the observed mechanical behavior can be attributed to the spatial redistribution of the occupied hybridized electronic states in the region between the transition metal atom and the chalcogens. Despite the strong covalent bonding between the transition metal and the chalcogens, we find that a simple linear relationship can be established to describe the dependence of the mechanical strength on the charge transfer from the transition metal atom to the chalcogens. Our studies suggest that these two-dimensional semiconducting TMDs can withstand large deformations, making them attractive for application in novel strain-engineered and flexible electronic and optoelectronic devices.