A comparative study of lattice dynamics of three- and two-dimensional MoS₂

This paper presents a comparative study of the lattice dynamics of three-dimensional layered MoS₂ and two-dimensional single layer MoS₂ based on the density functional theory. A comprehensive analysis of energetics and optimized structure parameters is performed using different methods. It is found that the van der Waals attraction between layers of three-dimensional (3D) layered MoS₂ is weak but is essential to hold the layers together with the equilibrium interlayer spacing. Cohesive energy, phonon dispersion curves, and corresponding density of states and related properties, such as Born-effective charges, dielectric constants, Raman and infrared active modes are calculated for 3D layered as well as 2D single layer MoS₂ using their optimized structures. These calculated values are compared with the experimental data to reveal interesting dimensionality effects. The absence of a weak interlayer interaction in 2D single layer MoS₂ results in the softening of some of Raman active modes.