First-principles insights into the stability and anisotropic properties of MoSe2 monolayer in biphenylene network

In this study, we conduct a comprehensive first-principles investigation of the structural, mechanical, electronic, and optical properties of the MoSe2 monolayer in biphenylene geometry (BPN-MoSe2). Our density functional theory-based results reveal that the BPN-MoSe2 monolayer is thermodynamically and mechanically stable, with notable structural anisotropy arising from the presence of inherent rectangular, hexagonal, and octagonal rings. Its dynamical and thermal stability is further confirmed by phonon dispersion and ab initio molecular dynamics simulations. Mechanical analysis indicates direction-dependent elastic behavior, demonstrating that the BPN-MoSe2 monolayer combines mechanical robustness with significant flexibility. The electronic band structure, calculated using the HSE06 hybrid functional, exhibits a narrow direct band gap of 0.23 eV, with the band edges predominantly composed of Mo-d and Se-p orbitals. Furthermore, we investigate the optical response of the material through the frequency-dependent complex dielectric function and absorption spectra. The anisotropic optical behavior is evident, with strong light absorption observed in both the visible and near-infrared regions. Overall, our findings highlight the potential of the BPN-MoSe2 monolayer as a promising candidate for next-generation two-dimensional flexible optoelectronic devices.