\(\hbox {Nb}_2\hbox {O}_5\) is a material of significant recent interest owing to its potential in diverse applications like photocatalysis, dielectrics, and energy storage. However, a lack of detailed experimental data on its various crystal structures hinders the selection of optimal polymorphs for specific functionalities. This work addresses this gap by presenting a comprehensive first-principles investigation into the electronic, dielectric, and optical properties of four key \(\hbox {Nb}_2\hbox {O}_5\) polymorphs. While standard density functional theory (DFT) calculations capture phase-dependent electronic trends, they often yield band gaps and optical spectra that deviate significantly from available experimental data. To overcome these limitations and achieve predictive accuracy, we employ advanced many-body perturbation theory, incorporating quasiparticle corrections. This approach provides reliable calculations of the electronic structure and optical response essential for understanding material performance. Our analysis reveals that the orthorhombic T phase, stable at lower temperatures, and the body-centered tetragonal P phase, stable at intermediate temperatures, exhibit particularly desirable properties. The T phase possesses a small calculated band gap (2.7 eV), significantly enhancing optical absorption in the near-ultraviolet and visible ranges, making it highly promising for photocatalytic and solar energy applications. Both T and P phases demonstrate notably low absorption onsets compared to other polymorphs, indicating superior light harvesting capabilities at lower energies. Their predicted photocatalytic potential surpasses that of common oxides like \(\hbox {TiO}_2\) and ZnO. This detailed understanding of the distinct electronic and optical behaviors among \(\hbox {Nb}_2\hbox {O}_5\) polymorphs highlights their diverse application potential and enables informed material design by correlating structure, stability, and functional properties.
