Dielectric Response of Hydrogenated Borophene Monolayers from First-Principles Density Functional Theory Calculations

Considering the incredible impact of 2D materials on emerging technologies, hydrogenated borophene (borophane) has attracted significant interest not only as a tunable platform for electronic and optoelectronic applications but also for its promising catalytic behavior. Here, we present a systematic density functional theory investigation of the structural, electronic, and optical properties of the 6,6 and 5,7 borophane polymorphs with distinct point-group symmetries. The calculated electronic band structures and density of states confirm the semimetallic characteristics of all structures, consistent with previous reports. The complex dielectric function spectra further reveal how structural motifs and hydrogenation patterns influence the onset of optical absorption. For the 5,7 HB monolayers, the first major absorption feature shifts markedly toward the far-infrared region compared with the 6,6 HB, indicating a stronger low-energy electronic response and a more pronounced metallic character. The optical spectra of 6,6 HB also show qualitative agreement with the available experimental UV-vis data. These results provide a comprehensive understanding of how symmetry and bonding topologies govern the electronic and optical behavior of borophane monolayers, offering useful guidance for the design of boron-based 2D optoelectronic materials.