A Systematic First-Principles Investigation of Structural, Electronic, Magnetic, and Thermoelectric Properties of Thorium Monopnictides ThPn (Pn = N, P, As): A Comparative Analysis of Theoretical Predictions of LDA, PBEsol, PBE-GGA, WC-GGA, and LDA + U Methods

Abstract

Thorium pnictides, besides their simple electronic structure, have been in the spotlight because of unique mechanical, electronic, and thermal properties. In this paper, we report on the first-principles calculations of structural, electronic, magnetic, and thermoelectric properties of thorium monopnictides ThPn (Pn =N, P, As) within density-functional-theory (DFT) formalism under ambient conditions. The equilibrium lattice parameters and bulk moduli are computed by fitting the total energy of the unit cell at various volumes into the Murnaghan’s equation of state. To compute the structural properties, we have employed all-electron full-potential linearized augmented plane wave plus local orbits (FP-LAPW + lo) method by treating exchange–correlation energy terms within local density approximation (LDA) and spin-polarized density approximation (LSDA). Moreover, a comparative analysis of DFT predictions on electronic structure is made with Wu–Cohen (WC) and Perdew–Burke–Ernzerhof (PBE) corrections to GGA as well as newly introduced PBEsol energy exchange–correlation functionals. For the electronic band structures, total and partial density of states, and magnetic moments of the compounds, however, we have implemented first time the LDA + U method to account for the possible strong correlation effects arising from the 5f electrons of Th atoms. On the other hand, Boltzmann transport theory is executed within relaxation time approximation, for the first-time reported thermoelectric properties of the compounds. Although the monopnictides have shown large values of thermoelectric power factor of the order of 1012 Wm−1·K−2·s−1, however, simultaneous higher values of thermal conductivity of the order of 1016 Wm−1·K−1·s−1 render them with lower values of thermoelectric efficiency. The small spin magnetic moments confirm the non-magnetic character of the monopnictides. The obtained results have been compared with the earlier theoretical and experimental studies.