Nonlinear optical response of Pristine and Halogen-Doped Diisopropylammonium Bromide: a theoretical approach

Recently, newly developed organic ferroelectric materials have garnered significant interest due to their suitability for electronic applications. Among these materials, diisopropylammonium bromide (dipaBr) stands out for its remarkable properties, exhibiting a spontaneous polarization of 23 μC/cm² and a high Curie temperature of 425 K, making it a promising candidate for practical applications. In this investigation, the nonlinear optical behavior of pristine and halogen-substituted diisopropylammonium bromide crystals was explored using density functional theory, aiming to elucidate the influence of chemical doping on the material's optical characteristics. The unmodified dipaBr structure was initially geometrically optimized, followed by a systematic replacement of the bromide anion with halogen atoms fluorine (F), chlorine (Cl), and iodine (I) to examine the resulting alterations in electronic configuration, molecular polarizability, and first hyperpolarizability (β), which are pivotal descriptors of second-order NLO effects. The computed NLO parameters reveal that the dipole moments for pristine and halogen-doped dipaBr are 18.96 D, 17.50 D, 10.18 D, and 11.41 D, respectively, as derived from the LANL2DZ basis set using CAM-B3LYP functional.

The nonlinear optical properties of pristine diisopropylammonium bromide (dipaBr) and its halogen-doped derivatives were investigated using Density Functional Theory (DFT). The computations were carried out using the B3LYP functional with the 6-31 + G(d), 6-311 +  + G(d,p), and LANL2DZ basis sets, together with the CAM-B3LYP functional employing the 6-311 +  + G(d,p) and LANL2DZ basis sets. The computational outputs were visualized using Gauss View 6 software. Halogen incorporation led to notable modifications in the electronic band gap and charge density distribution, with a marked increase in dipole moment and β values, particularly for the F- and I-substituted systems. Furthermore, the thermodynamic parameters of pristine and halogen-doped diisopropylammonium bromide are systematically analyzed.