Vibration response of monolayer 1H-MoTe2 to equibiaxial strain

Based on density functional theory and density functional perturbation theory calculations, we systematically investigate the vibration responses of monolayer 1H-MoTe2 to equibiaxial strains. It is found that, at the Γ point, the frequency shift of Raman-active modes (E′, A1′, and E″) and infrared-active modes (A2″ and E′) show domelike shapes; that is, their frequencies decrease monotonically under tensile strains but first increase and then decrease rapidly under compressive strains. The frequency-shift behaviors are revealed to come from vibration responses to both bond stretching and bond-angle bending in strained 1H-MoTe2. At the K point, a special acoustic mode becomes soft because its frequency drops to zero at a compressive strain of -11.27%. We find that electron occupancies in Mo dz2, Te px, and Te py orbitals weaken the vibration mode at K, which exhibits the in-plane vibration of Mo atoms and out-of-plane vibration of Te atoms. On the other hand, compressive strains enhance the Fermi surface nesting and abruptly soften the vibration frequency for one acoustic mode at K. Our results point out a way to detect the strain status of monolayer 1H-MoTe2 by measuring the vibration frequencies.