A DFT study to explore structural, elastic, mechanical, phonon, electronic and optical properties of halide perovskites AgXF 3 ( X = Be , Ca ) $$ {\mathrm{AgXF}}_3\left(\mathrm{X}=\mathrm{Be},\mathrm{Ca}\right) $$ with PBEsol, TB-mBJ and SCAN functionals

Abstract

First principles calculations have been performed using full potential linearized augmented plane wave, FP-LAPW, within Wien2k to elucidate structural, elastic, mechanical, phonon, electronic and optical properties of lead free halide perovskites ${\text{AgXF}}_3(X=\mathrm{Be},\mathrm{Ca})$. The energy volume curve fitting is used to examine structural stability. For structural optimization and mechanical properties, we employed Perdew–Burke–Ernzerhof generalized gradient approximation and PBEsol, revised for solids, exchange and correlation functional. The optimized lattice constant of ${\text{AgBeF}}_3$ and ${\text{AgCaF}}_3$ is 3.631 and 4.349Å. The elastic constant ${\text{C}}_{11}$, ${\text{C}}_{12}$ and ${\text{C}}_{44}$ are computed to extract different mechanical parameters like Poisson's ratio, Pugh's ratio, bulk modulus, shear modulus, Young's modulus, anisotropic ratio, Cauchy pressure and shear constant. The mechanical parameters exhibit greater structural, mechanical and dynamical stability of ${\text{AgBeF}}_3$ than ${\text{AgCaF}}_3$. The electronic and optical properties are calculated by using TB-mBJ and SCAN potentials in addition to PBEsol. The electronic band gap of ${\text{AgBeF}}_3$ and ${\text{AgCaF}}_3$ is 4.71 and 6.01 eV with TB-mBJ and both perovskites are indirect band gap materials. The optical response of these perovskites against wide range of incident electromagnetic radiation is assessed by calculating absorption, reflection, optical conductivity, dielectric constant, energy loss function and refraction. Strong absorption, high optical conductivity and low reflectivity indicates that ${\text{AgBeF}}_3$ and ${\text{AgCaF}}_3$ are promising materials for photovoltaic applications.