DOI: 10.5061/dryad.8gtht770d
title: DFT studies of the role of anion variation in physical properties of Cs2NaTlBr6-xClx (x = 0, 1, 2, 3, 4, 5, and 6) mixed halide double perovskites for optoelectronics

description: Halide-double perovskites have various benefits over lead-based
 perovskites due to their suitable optical absorption efficiency, higher
 stability, tunable bandgap, large carrier mobility, easy availability, and
 low cost. The structural, electrical, optical, and mechanical
 characteristics of the lead-free halide double perovskites Cs2NaTlBr6-xClx
 (x = 0, 1, 2, 3, 4, 5, and 6) are investigated by utilizing the
 first-principles density functional theory (DFT). The structural
 properties were computed at equilibrium, revealing that the crystals
 undergo structural phase transitions as the doping concentration varies.
 However, crystal stability was confirmed through the evaluation of the
 tolerance factor. The HSE06 functional is used to correct the bandgap
 underestimation by GGA-PBE. The band edge profile and electron density of
 states confirm the direct-bandgap semiconducting nature of the compounds.
 The bandgap increases approximately linearly with Cl incorporation,
 sharply tuned from 0.80–1.75 eV (GGA-PBE) and 1.78–2.98 eV (HSE06), making
 them highly suitable for photovoltaic and optoelectronic applications. The
 effective mass of electron ranges from 0.283m0 to 0.449m0, and the carrier
 mobility is from 83.913 cm2v-1s-1 to 305.485 cm2v-1s-1, respectively,
 suggesting excellent charge transport characteristics, essential for
 high-performance solar cells and photodetectors. The considered NaTL-based
 double perovskites have strong optical absorption in the visible and UV
 spectrum, with enhanced conductivity as Cl content increases. Binding
 energy analysis confirms strong lattice stability, with values decreasing
 from -3.193 eV (Br-rich) to -3.559 eV (Cl-rich), indicating improved
 thermodynamic robustness as Cl concentration increases. Mechanical
 analysis shows the ductile behavior of the considered perovskites,
 supported by Poisson’s ratio and Pugh’s modulus. The rising bulk modulus
 and Debye temperature with Cl incorporation enhance rigidity and thermal
 stability. These insights advance the anion-engineered design of stable,
 high-efficiency, lead-free NaTl-based perovskites for next-generation
 optoelectronic applications.
description: # DFT Studies of the Role of Anion Variation in Physical Properties of
 Cs2NaTlBr6-xClx (x = 0, 1, 2, 3, 4, 5, and 6) Mixed Halide Double
 Perovskites for Optoelectronics Dataset DOI:
 [10.5061/dryad.8gtht770d](10.5061/dryad.8gtht770d) ## Description of the
 data and file structure We conducted the theoretical and simulation study
 of mixed halide double perovskites Cs2NaTlBr6-xClx based on the density
 functional theory. We investigated the structural, mechanical, and
 thermodynamic stability of the considered materials and electronic and
 optical properties to determine the material's potential as a
 candidate for optoelectronics. In HBD_Mixed_anions.zip, the different data
 types folder is for two pure double perovskites, such as Cs₂NaTlCl₆ &
 Cs₂NaTlBr₆. Further, the Cl2Br4, Cl4Br2 (x = 2, 4) in ClxBr6-xData33 and
 ClBr5, Cl3Br3, Cl5Br (x= 1, 3, 5) in ClxBr1-xpart4 files are arranged
 for Cs2NaTlBr6-xClx mixed halide double perovskites. In each of the
 folders, readers will find the dataset for the calculation of structural
 optimization or relaxation files (SR), self-consistent calculations (STR),
 structural properties (STRUC), band structure (Band), hybrid band
 structure (HSE), density of states (DOS), effective mass calculation
 (eff_M), mechanical properties (Elastic), and optical properties (OPTIC).
 If someone wants to perform the calculations, they need to have experience
 at least in VASP or similar tools for first-principles calculations in
 computational materials science. ### Files and variables #### File:
 HBD\_Mixed\_anions.zip **Description:** In this submitted file, we
 included the data files to carry out the calculations using the Vienna
 ab-initio simulation package (VASP). We divided all the dataset in a
 specific folder name so that any one can track all the data. i. The four
 input files are always needed to perform a calculation in VASP. These
 files are POSCAR, POTCAR, INCAR, and KPOINTS. ii. OUTCAR stores all the
 information regarding the calculations steps. iii. The information about
 the total density of states and partial density of states in tdos.dat and
 PDOS_USER1.dat, PDOS_USER2.dat,
 PDOS_USER3.dat, PDOS_USER4.dat, PDOS_USER5.dat files, respectively within
 the DOS folder. iv. The bandgap related information will be found in
 BAND_GAP and for the illustration of the bandstructure, KLABELS,
 HIGH_SYMMETRY_POINTS, BAND.dat, REFORMATTED_BAND.dat are necessary files.
 v. We have used VPKIT.in file for calculations of the structural
 properties and effective mass of electron using different parameter
 settings. vi. In OPTIC folder, all the parameters such as real and
 imaginary dielectric function in real.in and IMAG.in, absorption
 coefficient in ABSORPTION.dat, extinction coefficient in EXTINCTION.dat,
 energy loss function in ENERGY_LOSSSPECTRUM.dat, reflectivity of the
 material in REFLECTIVITY.dat, and refractive index in REFRACTIVE.dat files
 are arranged with respect to energy (eV). ## Code/software To visualize
 the unit cell of the compound (POSCAR), we used Vesta software. Further,
 all the calculations can be done by the VASP simulation package.
 Matplotlib is used to visualize all the graphs in this research. The .dat
 file store the output data for the each calculation in respective folders
 with proper nametag with them. ## Access information Other publicly
 accessible locations of the data: * Not Applicable Data was derived from
 the following sources: * Vasp, Vaspkit, Vesta, Matplotlib