Bulk orthorhombic boron (o-B14) is an intriguing, recently predicted, three-dimensional (3D) boron allotrope. Its structure is characterized by edge-sharing pentagonal bipyramids, with diverse bond lengths. These structural motifs facilitate the formation of unusual seven-center-two-electron $\pi$ bonds, predicted for the first time in 3D boron allotropes. The presence of these bonds highlights the complexity and versatility of boron chemistry under ambient conditions. Moreover, this material is predicted to be a superconductor with a critical temperature $T_c$ of 29.1 K [Phys. Chem. Chem. Phys. 25, 15400 (2023)]. In the present work, we explore the electronic and optical properties of bulk o-B14 and its monolayer and bilayer forms, including hydrogen termination, using first-principles calculations. These two-dimensional structures are predicted to be dynamically stable and to exhibit a remarkable variety of electronic behavior including semiconductivity with a band gap of 0.67 eV (bilayer), superconductivity with a $T_c$ of 24.3 K (H-terminated bilayer), and magnetism (monolayer). The plasmonic and optical responses exhibit anisotropic behavior driven by the directional bonding network, as well as absorption in the visible region of the spectrum, which suggest promising opportunities for applications in advanced optoelectronic, plasmonic, and quantum devices.

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• Dielectric properties
• Electronic structure
• Ferroelectricity
• Superconductivity
• 2-dimensional systems
• Density functional theory
• First-principles calculations
• Linear response theory