Lattice dynamics, elastic, magnetic, thermodynamic and thermoelectric properties of the two-dimensional semiconductors MPSe3 (M = Cd, Fe and NI): a first-principles study

Abstract

Adopting Density Functional Theory (DFT) with Hubbard U correction implemented in Quantum Espresso, we have performed a comprehensive first-principles study of MPSe _3 (M = Cd. Fe and Ni) monolayers. The computed electronic properties revealed the semi-conductive nature of the monolayers with small indirect bandgaps. A free-standing single layer of MPSe _3 can be exfoliated from the parent compound by virtue of its structural stability and high in-plane stiffness. Hence, the elastic and dynamical properties were computed to establish the mechanical and dynamical stability. The results showed that CdPSe _3 and NiPSe _3 are stable in the trigonal structure while a single negative frequency observed in the phonon dispersion of FePSe _3 indicates the possibility to relax to another, less symmetric structure. In addition, these 2D systems showed relatively good response when subjected to strain hence, they can be said to be mechanically stable. The thermodynamic properties, such as internal energies, vibrational free energies, entropies and constant-volume heat capacities have been computed within the harmonic approximations using the phonon density of states. The computed thermoelectric properties show that CdPSe _3 and FePSe _3 have the peak figure of merit at low temperature of 50 K. This work predicts a thermoelectric performance with an electronic figure of merit of 0.28 for p-doped CdPSe _3 . Moreover, the DFT+U method predicts an electronic figure of merit of 0.39 and 0.2 for p-doped FePSe _3 and NiPSe _3 , respectively.

Keywords

• 2D materials
• first-principles calculations
• thermoelectrics
• vibrational properties