A Computational Outlook on Ferroelectricity: Transition State Optimizations and Charge Analysis

Undergraduate #33
Discipline: Chemistry and Chemical Sciences
Subcategory: Chemistry (not Biochemistry)

Moises Romero - California State University San Bernardino
Co-Author(s): Daniel Miller and Eva Zurek, University at Buffalo, Buffalo, NY

Ferroelectricity is a property of certain compounds that contain a spontaneous polarization which can be reversed with the application of an electric field. Croconic acid and 1,4-diazabicyclo[2.2.2]octane (DABCO) are strong organic ferroelectrics due to their high spontaneous polarization; however, DABCO’s ferroelectric activities are only viewed in certain cocrystals. Both materials’ ferroelectric activity is related to their proton transfer mechanisms. Prior studies on croconic acid’s proton transfer transition states have been performed; however the theoretical calculations were based on an interpolated transition state, and found only one possible reaction pathway. This study seeks to contrast the interpolation method from the prior studies with the nudged elastic band method (NEB), which is a more thorough method for predicting for the lowest energy pathway. Vienna ab initio Structure Program (VASP) was used to perform the calculations using several pseudopotentials; Avogadro, and XCrySDen were used to view the results. Results for DABCO showed the interpolation method having an energy barrier of .32eV; however the NEB method predicted two pathways with lower energy barriers of .26eV and .24eV. Results for croconic acid using the interpolation method showed an energy barrier of 1.15eV and NEB method an energy barrier of .56eV. All three new pathways had reduced symmetries compared to interpolation. Charge density differences (CDD) were calculated for the structures to show the hydrogen bond interaction and electron density differences within each method. Polarization was calculated for each structure: croconic acid having a calculated polarization of 19.74°C/cm2 with the interpolation method and 26°C/cm2 with the NEB method; the experimental value of 21°C/cm2 lies between these values. DABCO had calculated polarizations of 0.10°C/cm2 (interpolation), 0.07°C/cm2 (NEB pathway one), and 0.18°C/cm2 (NEB pathway two).

Funder Acknowledgement(s): NSF-HRD 1435163, CSUSB Center for Materials Science

Faculty Advisor: Kimberley Cousins, kcousins@csusb.edu

Role: I performed all the computational calculations. I then took the calculations and tabulated the data and created figures. Analysis of data was done by graduate student Daniel Miller.