Cationic substitution, dynamical stability, thermal stability, electronic and thermoelectric properties in 2D dialkali metal monoxides via DFT and ML approach

Abstract

Abstract Using the WIEN2k software, Density Functional Theory (DFT) was applied to analyse the impact of cationic substitution on the physical features of the 1T-K2O monolayer. Phonon dispersion analysis confirmed dynamical stability, Ab-initio Molecular Dynamics (AIMD) simulations validated thermal stability, and cohesive energy calculations ensured thermodynamic stability of 1T-K2O. Based on the phonon studies, both 1T-KNaO and 1T-KRbO are dynamically unstable with a slightly visible imaginary frequency. Specifically, for electronic property assessment, generalized gradient approximation (GGA) and hybrid exchange-correlation functionals were utilized. This study unveiled the 1T-KXO (X = Na, K, Rb) monolayers as an indirect band gap semiconductor, for 1T-K2O, 1T-KNaO and 1T-KRbO were 0.94 eV (1.84 eV), 1.03 eV (1.94 eV) and 0.84 eV (1.77 eV) obtained implementing GGA and hybrid functionals, respectively. Using a machine learning (ML) approach, the band gap was predicted as 1.45 eV (0.85 eV) for 1T-K2O, 1.79 eV (0.97 eV) for 1T-KNaO, and 1.17 eV (0.72 eV) for 1T-KRbO, with random forest regression (linear regression) method. The physical properties were tailored by the impact of cationic substitution on the 1T-K2O were studied. The variation in the physical properties were investigated. Optical analysis indicated a strong absorption coefficient, underscoring the 1T-KXO monolayers potential for photovoltaic applications in the UV region. The ZT value obtained at room temperature are 0.58, 0.86 and 0.69 for 1T-K2O, 1T-KNaO and 1TKRbO, respectively. Additionally, the 1T-KNaO demonstrated promising thermoelectric properties, at 400 K achieving a figure of merit (ZT) of 0.93, indicating its suitability for waste heat recovery. A ML model was trained to predict the ZT of 1T-KXO using random forest regression and linear regression.