Transition Metal Dichalcogenides (TMDs) are characteristic of a class of emerging materials which can occur in several phases, such as: 1H, 1T and 1T'. Depending on their polymorphic form, these materials present different structural properties. Thus, using the density functional theory (DFT) invented in the CASTEP computational code, we investigated the structural, electronic and vibrational properties of the monolayers of chromium disulfide (CrS2), molybdenum disulfide (MoS2) and tungsten disulfide (WS2). We performed the calculations using the approaches based on the generalized gradient approximation (GGA) and local density approximation (LDA). In this study, we verified that the 1H and 1T' phase presents stability in its phonon dynamics. However, the 1T phase revealed instability presenting imaginary modes in the phonon dispersion, in agreement with the literature data. Our simulations demonstrate that monolayers in the 1H phase are a direct bandgap semiconductor and in the 1T’ phase a semimetal.
Pereira et al. (Tue,) studied this question.