DFT and DFPT calculations of the structural, electronic, optical, vibrational and thermodynamic properties of silicon tetraborate

In this study, the structural, mechanical, electronic, optical vibrational, and thermodynamic properties of a new crystalline material, silicon tetraborate (SiB4O7), were calculated using DFT and DFPT. This material may prove crucial for the development of devices with particular optical and electronic properties. We report here that the band gap calculated for SiB4O7 using the GGA-PBE functional was Eg = 3.922 eV which is consistent with the values found in the literature for similar materials, such as PbB4O7. The band gap energy calculated using the HSE06 hybrid functional was Eg = 5.120 eV. Six prominent peaks were observed in the optical absorption spectrum of SiB4O7. Based on the optimized structures, the elastic stiffness constants and the elastic compliance of the system were calculated using the stress-strain method. The mechanical properties of the orthorhombic-SiB4O7, including the mechanical moduli (bulk modulus, shear modulus, Young's modulus, Poisson's ratio, and anisotropy), were evaluated using the Voigt-Reuss-Hill approach. The mechanical and vibrational properties, thermodynamic potentials, and calculated constant-volume specific heat can be used to predict the stability of the crystal phase. The breakthroughs and insights presented herein for this new material may help in the development of optoelectronic devices.