DFT study on geometries, electronic structures and electronic absorption of Naphthalene

This study introduces a novel quantum computational approach using Density Functional Theory (DFT) with multiple basis sets (particularly 6-31G) to examine naphthalene's structural and electronic characteristics. Key theoretical investigations include, Frontier molecular orbitals (HOMO-LUMO), Electronic band gap (E₉), Density of states (DOS), UV absorption spectra, Natural Bond Orbital (NBO) analysis, Thermochemical properties under standard conditions and Optical properties, including direct/indirect transition band gaps. Employing DFT/6-31G with a fixed HOMO-LUMO gap of 4.75 eV, our results demonstrate strong consistency with recent DFT studies reporting gap values of 4.71, 4.873, and 4.74 eV, respectively. The geometric, electronic, and optical properties—including polarizabilities and hyperpolarizabilities—of Naphthalene, is investigated using Density Functional Theory (DFT) with the B3LYP hybrid functional. Additionally, the Ultraviolet-Visible (UV-Vis) spectra were analyzed using a time-dependent (TD) DFT approach (TDSCF-DFT/B3LYP), which incorporates many-body effects and dynamic interactions under time-dependent potentials. The electronic absorption features in the visible and near-UV regions were computed, plotted, and assigned based on TD-DFT calculations.