Molybdenum disulfide under extreme conditions: An ab initio study on its melting

Abstract

Crystalline molybdenum disulfide has become a central actor in the 2D-materials community due to its promising optoelectronic and thermoelectric properties. Despite the extensive work made in investigating these properties, a vast area of knowledge remains unknown on the structure and dynamics of its disordered phases such as liquid and amorphous. Thus, the goal of this work is to investigate the melting of bulk molybdenum disulfide using ab initio molecular dynamics based on density functional theory. We employ the two-phase and Z-methods to evaluate the melting in a number of conditions. Our results at 1 bar reveal that the two-phase procedure is preferred since it predicts a melting point of 2266.92 K that is directly computed using simulations at constant pressure and energy. In contrast, this temperature is indirectly estimated at 2154.01 K with the Z-method using an interpolation of simulations at constant volume and energy. Nevertheless, we find that both methods are complementary as they allow computing different thermodynamic and structural properties. For instance, we estimate a melting heat of 0.67 eV/atom with the two-phase coexistence route, which shows very good agreement with the value of 0.75 eV/atom obtained from the difference of the internal energies of separate crystalline and liquid ensembles at the same conditions of 1 bar and 2266.92 K. In contrast, the Z-method allows us to determine the influence of pressure on the melting temperature, density, and coordination number with a lower computational cost.