Theoretical Investigation of the Static Behavior of Various Compositions of Layered Quaternary Oxysulfide Compounds, A New Possibility for Next-Generation Supercapacitive Energy Devices

In this work, detailed first principles density functional theory (DFT) calculations have been performed to investigate structural, electronic, optical, thermodynamic and mechanical properties for layered quaternary oxysulfide compounds LaXSO (X [Formula: see text] Cu, Fe, Mg and Zn) in order to explore their potentials for energy storage applications. Among all compounds, LaCuSO exhibits semiconducting behavior with a band gap of 2.19[Formula: see text]eV as by DFT[Formula: see text]U approach, whereas LaFeSO, LaMgSO and LaZnSO have displayed metallic characteristics. Spin-polarized electronic properties have shown greater influence on the band structure of these materials, especially for LaCuSO compound, which shows states at Fermi level due to spin influence on Cu-d state. Optical properties are consistent with the electronic results, notably LaFeSO shows very high values of dielectric response (47.89) and refractive index (6.5), indicating significant polarizability. Thermodynamic stability is confirmed by the absence of any imaginary phonon frequencies and the Debye temperature indicates sustainability of the compounds to work under extreme conditions. Mechanical instability is observed in LaMgSO and LaZnSO compounds due to larger negative [Formula: see text] values while LaCuSO and LaFeSO have turned out to be highly mechanically stable with high stiffness and brittle nature. These features highlight the potential of LaCuSO and LaFeSO compounds as promising candidates for pseudocapacitive or hybrid supercapacitor electrodes.