Hydrogen Placement on Potential Organic Ferroelectric NUBHOH

RM 215

NUBHOH is an organic potential ferroelectric co-crystalline material composed of glycine and urea, with a reported crystallographic space group of P2_1 for the non-hydrogen atoms. A ferroelectric material is one that can switch its polarization state once an electric field is applied. The polarization switch on an organic ferroelectric has practical uses like memory storage in electrical devices. One mechanism for a polarization switch is through hydrogen bond transfer. NUBHOH has no hydrogens present on its reported structure found in the Cambridge Data Base. This project tried to find possible hydrogen placements on the glycine component of urea because it can exist as a zwitter ion or in neutral form. Vienna Ab initio Simulation Package (VASP) was used to run plane wave density functional calculations from different starting protonation states, and visualization was accomplished using Mercury, VMD and Avogadro software. These structures were subject to geometry optimization, as well as molecular dynamics simulation, with everything relaxed, on NUBHOH. These calculations found the lowest energy stable state was one in which the protons on glycine and urea form four unique species, and each glycine no longer exists as either a zwitter ion or neutral molecule. This structure has no remaining crystallographic symmetry (P1 space group), as well as intriguing potential for electroactive behavior via proton behavior coupled with bond and molecular rotation.