Strain Engineering of Two-Dimensional Penta-Octa B4C2N3: Electronic Structure and Optical Response

Two-dimensional (2D) boron–carbon–nitrogen (BCN) systems have recently attracted significant interest owing to their structural stability, electronic diversity, and tunable optical behavior. In this work, the structural, electronic, and optical properties of the 2D penta–octa B4C2N3 monolayer are systematically investigated using first-principles calculations. The optimized structure exhibits moderate buckling, multiple distinct bond environments, and energetically favorable cohesive and formation energies. The monolayer is identified as a non-magnetic indirect semiconductor with a band gap of 0.279 eV, where the density of states is dominated by N–p and C–p orbitals. Thermal stability is confirmed by ab initio molecular dynamics simulations at 600 K, and a relatively high work function of 5.272 eV suggests strong surface stability and favorable compatibility with electronic interfaces. Biaxial strain is shown to be highly effective in tuning the electronic structure. Compressive strain (-4% to -2%) induces a semiconductor-to-metal transition, while moderate tensile strain (+1% to +3%) results in an indirect to direct band gap conversion. The band gap can be continuously tuned from 0.11 eV to 0.583 eV under tensile loading. Optical absorption calculations reveal strong light–matter interaction with absorption coefficients reaching 104–105 cm-1. These results demonstrate that 2D penta–octa B4C2N3 is a structurally robust, electronically adaptive, and optically responsive monolayer with strong potential for next-generation strain-engineered optoelectronic and photonic devices.