A robust first-principles study of structural, mechanical, electronic, and optical properties of Be0.75Cd0.25X and Be0.5Cd0.25Zn0.25X (X = S/Se/Te) chalcogenides

This paper presents a comprehensive first-principles study of Be 0.75 Cd 0.25 X and Be 0.5 Cd 0.25 Zn 0.25 X, comparing them with BeX (X = S, Se, and Te) chalcogenides. The strictest convergence criteria have been imposed using the PBE-GGA exchange-correlation function to study structural stability and mechanical properties. Whilst the hybrid-HSE06-XC functional, which treats the electronic structure with higher accuracy than other XC functionals, albeit at the cost of increased computational time, is employed to analyze the electronic state, band structure, and optical characteristics in the CASTEP platform. The calculated band gaps of the pristine BeX compounds are in good agreement with their experimental values, with deviations of only 8-10.2%, which provides a basis for the electronic structure analysis of the above-mentioned chalcogenide materials. Born stability criteria for elastic constant calculations and the absence of imaginary phonons confirm the structural stability of these chalcogenides. The presence of Cd 2+ and Zn 2+ has resulted in a narrower band gap (1.89 eV, the lowest for Be 0.5 Cd 0.25 Zn 0.25 Te) and an indirect-to-direct band-gap transition in Be 0.5 Cd 0.25 Zn 0.25 S and Be 0.5 Cd 0.25 Zn 0.25 Se, making them suitable for photovoltaic and optoelectronic devices. Optical analysis shows higher dielectric constants (DF) for the chalcogenides in the IR, VIS, and lower UV regions (static DF). \(\:=5.86\) being the highest for Be 0.5 Cd 0.25 Zn 0.25 Te) compared to their pristine state, indicating lower exciton binding energy. Also, higher optical conductivity and lower loss function of these alloyed compounds suggest stronger electromagnetic polarization and stronger light absorption. Hence, these six novel chalcogenides, formulated and characterized, exhibit enhanced electronic and optical properties, opening a domain for further research on these materials and providing critical guidance for experimentation aimed at real-world applications.