An investigation of dynamical stability, electronic, and optical properties of sodium metaborate (NaBO2): A many-body G0W0+BSE approach

Abstract

This study investigated the electronic, optical, and phonon properties of bulk sodium metaborate (NaBO2) using density functional theory (DFT), and the many-body G0W0 plus Bethe-Salpeter equation (BSE) approach. The investigation of the phonon dispersion curve indicates the dynamic stability of the NaBO2 compound in the rhombohedral phase, which is in good agreement with experimental results. Also, cohesive energy calculation shows the thermodynamic stability of this material. The band structure results indicated that the direct band gap of NaBO2 at the Γ point is 3.81 eV/4.16 eV within LDA/PBE approximation, which increased to 6.78 eV/6.57 eV by considering the quasi-particle effects in G0W0@LDA/PBE calculations. Considering the electron-hole effects in the G0W0+BSE approach, the optical gap showed more accurate results, and the value of 5.83 eV/5.71 eV was obtained for the LDA/PBE starting point. Therefore, excitonic effects within the G0W0+BSE approximation, in comparison to G0W0+RPA, leads to the redshift of the optical absorption spectrum. The optical results estimate the exciton binding energy of 0.95 eV/0.86 eV within LDA/PBE approximation. The investigation of the optical absorption spectrum introduces sodium metaborate as a transparent material with the prospect of use in optical devices.