Wannier-Mott excitons in alkali metal-based nitridorhenate: A DFT study

Abstract

To better understand the electronic, structural, optical, and transport properties of the alkali metal-based nitridorhenate (Li 5 ReN 4 ), first-principles calculations were performed using the full potential linearized augmented plane wave (FP-LAPW) method within the generalised gradient approximation (GGA) framework. The ground-state properties were computed for an orthorhombic structure (Pmmn-59). Both the band structure and the total density of states were carried out. Based on the band structure, the Li 5 ReN 4 compound is a direct band semiconductor with a bandgap value of 2.68 eV. In addition, the optical properties were calculated, indicating that lithium nitridorhenate is a highly absorbent material. The effective masses of the electrons and holes were calculated. Also, we investigate the connection between exciton binding energy and band structure. Moreover, the exciton for Li 5 ReN 4 is a weak exciton of the Mott-Wannier type. Furthermore, the transport properties were investigated using the semi-classical Boltzmann theory as implemented in the BoltzTraP code. Owing to its semiconducting nature, the material has a high Seebeck coefficient (S) of 287 μV/K at 300 K. At 300 K and 400 K, the predicted thermoelectric figure of merit was 0.790 and 0.802. Each of these results shows that our compound is a strong choice for applications in photovoltaic, optoelectronic, and thermoelectrical devices. Additionally, based on the observation of thermoelectric figure of merit, the Li 5 ReN 4 compound is also suitable for waste heat regeneration or waste heat recovery process. The calculated charge density distribution of Li 5 ReN 4 along (011).