Scandium and Titanium doped hexamine for remarkable nonlinear optical properties: a DFT study

This study explores the nonlinear optical (NLO) properties of hexamine (HMT) doped with transition metals scandium (Sc) and titanium (Ti), exhibiting enhanced NLO responses for advanced photonic devices. Employing ωB97XD functional for optimization and calculations, the study examines geometric parameters, electronic excitation, exciton binding energy (E_b), and vertical ionization energy (VIE) using DFT and TD-DFT. High VIE (3.25 to 4.52 eV) indicates enhanced stability in doped systems. The HOMO-LUMO gap decreases from 10.69 eV in pure HMT to 3.30 to 4.85 eV in the designed systems. These systems exhibit thermodynamic stability with binding energies 3.51 to 4.27 kcal/mol, and Ti-HMT-Ti being the most stable. A two-level approximation method is utilized to determine linear polarizability and nonlinear first and second hyperpolarizability (α_static, β_static, γ_static), which exhibits the highest γ_static (6546.63 au) value of Sc-HMT-Sc. Orbital transitions, charge distribution, electrophilicity, and nucleophilicity are examined using TDM, EDDM, and ESP, respectively. PDOS and TDOS provide insights into HOMO-LUMO gap reduction, NCI identifies the weak interactions and broadened and red-shifted UV absorption spectra, all are in the favour of NLO response of designed complexes. So, these materials show exceptional NLO properties and promising for optoelectronic applications.