(b)

1. Van der Waals interactions in an organic ferroelectricDavid H. Vanderbilt, Rutgers University, DMR 0801343 One of the most successful methodologies for realistic computations on materials is density-functional theory (DFT), in which the electrons are assumed to move in a mean-field potential that effectively incorporates exchange and correlation effects. Conventional exchange-correlation (XC) potentials are not capable of treating van der Waals (vdW) interactions.. Under this grant, we have previously developed a series of XC potentials that provide an increasingly reliable description of the vdW interactions, culminating in the formulation of our so-called vdW-DF2 functional. We have shown this to be very successful in describing weak intermolecular interactions, as for example between DNA base pairs, and even for challenging problems like the physisorption of molecules on metal surfaces. Here we show that vdW-DF2 also gives dramatic improvements in the description of proton transfer in certain classes of organic ferroelectrics. In addition to correcting the equilibrium intermolecular separation as expected, vdW-DF2 also greatly improves the energy difference and barrier associated with the proton transfer, a property for which it is not as obviously well suited. This provides yet more support for the general utility and promise of the vdW-DF2 approach. (b) (c) (d) Organic ferroelectric Phz-H2ca. (a) Structure of organic crystal composed of Phz (triple-ring) and H2ca (two-armed) molecules. Light blue arrows show proton transfer that is responsible for the ferroelectric transition. (b-d) Close-up showing three stages in the proton transfer process.

2. Van der Waals interactions in an organic ferroelectricDavid H. Vanderbilt, Rutgers University, DMR 0801343 http://www.physics.rutgers.edu/~dhv/uspp Broader impacts: • Web sites maintained for general community use (see at right): • Ultrasoft Pseudopotentials • Wannier 90 • Contributions to open-source software packages • ABINIT • PWSCF (Quantum Espresso) • Service on scientific committees for international conferences including: • 15th International Workshop on Computational Physics and Materials Science, Trieste, Italy, 13-15 January, 2011 • Co-organizer, CECAM Workshop on Topological Insulators and Non-Perturbative Spin-Orbit Coupling, Lausanne, Switzerland, Jan. 9-11, 2012. USPP: Software for generating ultrasoft pseudopotentials, and library of input files for most elements in the periodic table. http://www.wannier.org Wannier90: Software for constructing maximally localized Wannier functions (with A.A. Mostofi, J.R. Yates, Y.-S. Lee, I. Souza, and N. Marzari)