A first-principles study of the thermodynamic and vibrational properties of ReS₂under pressure

Two-dimensional layered materials (2DMs) are promising candidates for novel devices due to their tunable properties. The properties can be tuned by e.g. controlling the number of layers or applying external pressure on the structures. In order to control the (tuned) properties exactly, precise characterization of 2DMs' is needed. Here, the effect of hydrostatic pressure on the structural, energetic, electronic, and vibrational properties of layered bulk ReS₂ was studied using density functional theory. The electronic band gap of the 1T phase is shown to undergo a nearly-direct to indirect transition at about 9 GPa, while the 1T' phase is found to remain a robust nearly-direct band gap material under pressure. The computational analysis of the vibrational properties of both ReS₂ phases reproduced existing experimental Raman spectroscopy data for ω vs. P trends and provided a path towards an accurate phase discrimination using infrared spectroscopy, inelastic neutron, and X-ray scattering.