Effect of non-local hybrid functional on electronic band structure, manipulation of photocatalytic properties and optical response of Cu alloyed NaMgF3

Abstract

In the context of eco-friendly renewable hydrogen energy production, it is imperative to compute the band edges positions and the effect of dopant concentration on the energy-harnessing capability of a designed photocatalyst. Ergo we investigated NaMgF3 fluoro-perovskite due to its novel and intriguing optical properties using Density functional theory (DFT). The impact of Cu on the band edge positions of NaMgF3, structural, electronic, and optical features is explored herein using Perdew-Burke-Ernzerhof generalized gradient approximation (GGA-PBE) and Ultrasoft pseudo potential (USSP) method. Electronic properties have been computed with Heyd–Scuseria– Ernzerhof (HSE03) hybrid functional to get experimentally comparable results, when sodium was replaced by Cu in NaMgF3 fluoro-perovskite up to 100%. The lattice parameters (a = b) show a quasi-linear increasing trend while alloying with Cu unlike the c-lattice parameter, which first increases and then decreases for Cu concentration above 40%. A cubic to pseudocubic tetragonal transition was also seen as a result of Cu inclusion at the Na site. The Bandgap enhancement of 7.393 eV is observed for HSE03 hybrid potential for pristine NaMgF3, in contrast with its GGA-PBE counterpart (5.75 eV). In addition, the band gap topology is found to be consistent for local and nonlocal hybrid potentials and shows decreasing trend upon alloying with Cu. The reduction in band gap infers the location of CBE just below the reduction edge of NHE for 33% Cu inclusion in NaMgF3 and hence is considered a suitable alloying concentration for the photodegradation of chemical dyes. Optical properties such as absorption, reflectivity, refractive index, dielectric function, and energy loss function were computed and an apparent red shift was observed after Cu inclusion. The static refractive index and dielectric function for pure NaMgF3 were found to be 1.45 and 1.95 respectively, and a linear behavior was observed after alloying in all optical parameters. Hence Cu alloyed NaMgF3 can possess possible future applications in optoelectronic and energy devices.