Piezoelectric hydrogen bonding: computational screening for a design rationale.

Organic piezoelectric materials are promising targets in applications such as energy harvesting or mechanical sensors and actuators. In a recent paper (Werling, K. A.; et al. J. Phys. Chem. Lett. 2013, 4, 1365-1370), we have shown that hydrogen bonding gives rise to a significant piezoelectric response. In this article, we aim to find organic hydrogen bonded systems with increased piezo-response by investigating different hydrogen bonding motifs and by tailoring the hydrogen bond strength via functionalization. The largest piezo-coefficient of 23 pm/V is found for the nitrobenzene-aniline dimer. We develop a simple, yet surprisingly accurate rationale to predict piezo-coefficients based on the zero-field compliance matrix and dipole derivatives. This rationale increases the speed of first-principles piezo-coefficient calculations by an order of magnitude. At the same time, it suggests how to understand and further increase the piezo-response. Our rationale also explains the remarkably large piezo-response of 150 pm/V and more for another class of systems, the "molecular springs" (Marvin, C.; et al. J. Phys. Chem. C 2013, 117, 16783-16790.).

Piezoelectric Effects of Applied Electric Fields on Hydrogen-Bond Interactions: First-Principles Electronic Structure Investigation of Weak Electrostatic Interactions.

The piezoelectric properties of 2-methyl-4-nitroaniline crystals were explored qualitatively and quantitatively using an electrostatically embedded many-body (EE-MB) expansion scheme for the correlation energies of a system of monomers within the crystal. The results demonstrate that hydrogen bonding is an inherently piezoelectric interaction, deforming in response to the electrostatic environment. We obtain piezo-coefficients in excellent agreement with the experimental values. This approach reduces computational cost and reproduces the total resolution of the identity (RI)-Møller-Plesset second-order perturbation theory (RI-MP2) energy for the system to within 1.3 × 10(-5)%. Furthermore, the results suggest novel ways to self-assemble piezoelectric solids and suggest that accurate treatment of hydrogen bonds requires precise electrostatic evaluation. Considering the ubiquity of hydrogen bonds across chemistry, materials, and biology, a new electromechanical view of these interactions is required.