Computational and Data‐Driven Exploration of Structural, Optical, and Photocatalytic Behaviors in Lead‐Free Cs 2 GeX 6 (X = F, Cl, Br, and I) Double
Sudip Dey Dipta, Tanwi Chakraborty, Anoy Chakraborty, Uddhob Banik, Md Rasidul Islam, Md Masud RanaABSTRACT
The structural, electronic, optical, mechanical, thermodynamic, and photocatalytic properties of lead‐free double halide perovskites Cs 2 GeX 6 (X = F, Cl, Br, and I) are investigated in this study using a first‐principles approach by machine learning (ML). The CASTEP‐obtained optimized cubic Fm‐3m structures show systematic lattice expansion as the halogen size increases. A narrowing of the band gap from 5.91 eV (Cs 2 GeF 6 ) to metallic behavior in Cs 2 GeI 6 is revealed by electronic calculation, demonstrating the significant impact of halogen electronegativity. For heavier halides, optical results reveal higher dielectric constants and red‐shifted absorption edges. According to mechanical analysis, Cs 2 GeI 6 is ductile while Cs 2 GeCl 6 is brittle. Dynamical stability is confirmed by phonon dispersion. According to band calculations, Cs 2 GeF 6 and Cs 2 GeCl 6 are appropriate for general water splitting. The Debye temperature decreases from F to I substitution, according to thermodynamic results. In order to predict the band gap, five ML regression models were trained using the structural features obtained from our DFT experiment, which were Lattice Parameter, Volume, Tolerance Factor, Octahedral Factor, and Formation Energy. XGBoost achieved 99.47% accuracy but severe overfitting, whereas Lasso achieved 92.80% accuracy with minimal overfitting, demonstrating greater reliability.