Predicting Potential Polarization for Novel Fluorinated Diisopropylammonium Bromide (DIPAB) Systems

SMSU Event Center BC

Diisopropylammonium bromide (DIPAB) is an organic molecular ferroelectric crystal processed from aqueous solution with a spontaneous polarization of 23 C/cm2, comparable to the commercially used inorganic ferroelectric barium titanate (BTO). Ferroelectrics are highly desirable for their environment friendly quality and their commercial uses such as electro-optic materials for data storage applications, mechanical flexibility, ferroelectric thin-film memories and actuation. One of the properties of ferroelectric materials is that it exhibits spontaneous electric polarization that can be reversed by an applied electric field. The purpose of this study is to investigate if the ferroelectric properties of diisopropylammonium bromide increases by the replacement of its hydrogen atoms with a more electronegative atom such as fluorine. This task is performed by studying three different methods for calculating atomic charges available in the molecular modeling software Spartan ‘16, such as electrostatic, Mulliken and natural orbitals for different systems. The geometry of the system used was extracted from the crystal structure for DIPAB. The basis set study was performed by calculating energies and electron densities, using density functional (wB97x-D) theory along with two different basis sets: 6-31G* and 6-311+G**. The data was obtained for ten different molecular systems using both basis sets (6-31G* and 6-311+G**). In order to understand the data, we first focused in analyzing the three different atomic charges assignments methods for the ten systems, examining specifically the calculated charge on the nitrogen atom of the DIPAB system. The difference of the atomic charges of nitrogen atom was determined, between the original structures minus the novel fluorinated system. The Mulliken and natural orbital methods showed the smallest differences while the electrostatic method gave the largest differences in the systems with fluorine compared to the known system DIPAB. Also, the system with the highest atomic charge difference for all methods, was the one in which all hydrogen atoms were replaced with fluorine, as predicted. In future work, larger clusters of the fluorinated DIPAB systems, along with the entire solid state system will be modelled, to predict if, indeed one or more the fluorinated derivatives will have increased polarization compared to the known system, and therefore increased spontaneous polarization needed for ferroelectric applications.