Comparison of vibrational and thermodynamic properties of MoS2 and WS2 nanotubes: first principles study

Abstract

Hybrid density functional theory investigations are conducted to compare the structural properties, stability, vibrational frequencies, and thermodynamic functions of MoS2 and WS2-based monolayers and single-wall nanotubes using the same calculation scheme. The thermal contributions to thermodynamic functions for the layers and nanotubes are computed using phonon frequencies in the harmonic approximation. The thin MoS2 and WS2 nanotubes’ thermodynamic properties in regard to the same properties of the corresponding monolayers are obtained. It is found a noticeable deviation in these relative thermodynamic properties of the MoS2 and WS2 nanotubes. It is also shown that the thermal contribution to the stability of nanotubes is appreciable, especially for the nanotubes with small diameters. The deviation of nanotube free energy, entropy, and heat capacity from the layer values is larger in the case of MoS2 than in the case of WS2.