Ab-initio investigation of the structural stability, electronic and optical properties of the LiBO2 compound by using the G0W0+BSE approach

Abstract

This article investigates the structural stability, and electronic and optical properties of the LiBO2 compound using density functional theory (DFT) and solving the many-body Bethe-Salpeter equation within the G0W0+BSE approach. The structural properties showed that the monoclinic structure of LiBO2 is thermodynamically and dynamically stable within both LDA and GGA approximations. The band structure results indicated that the direct band gap of LiBO2 at the Γ point is 6.05 eV, which increased to 8.95 eV by considering the quasi-particle effects in G0W0@LDA calculations. The maximum reflectance in the x, y, and z directions is 0.48, 0.86, and 0.54, respectively, with the corresponding static refractive index values of 1.52, 1.61, and 1.54. The direct optical band gap obtained from the imaginary part of the dielectric function is 5.95 eV, 5.95 eV, and 6.10 eV for the various directions x, y, and z respectively. Considering the electron-hole effects in the G0W0+BSE approach, the optical gap showed more accurate results, and the value of 7.54 eV was obtained in the x and z-directions and 8.10 eV in the y-direction. Therefore, excitonic effects within the G0W0+BSE approximation, in comparison to G0W0+RPA, leads to the redshift of the optical absorption spectrum. The calculated exciton binding energy is 1.41 eV for the x and z-directions and 0.85 eV for the y-direction. Finally, it can be stated that LiBO2 is a wide-gap insulator with a gap greater than 7 eV in the monoclinic structure. This indicates the high transparency of the LiBO2 crystal, with the prospect of application in optical instruments.