{\it A Priori} Method for First Principles Study of Aqueous Electrochemistry: Application to Biofuels and Catalysis

We present a novel description of water which will allow the first {\it a priori} studies of catalysis of biofuels in aqueous electrochemical environments. Our method offers a computationally efficient alternative to the thermal sampling required by molecular dynamics yet provides a more realistic description of bulk water than including explicit frozen water or traditional continuum solvation models. Into Joint Density Functional Theory (JDFT), which joins an electron density-functional for the solute with classical density-functional theories for liquid water\footnote{R. Sundararaman et al, unpublished, to be presented at the APS March Meeting (2011)} into a single variational principle for the free energy of the combined system, we introduce the innovation of an {\it a priori} form of the coupling functional between the quantum-mechanical system and liquid water based on a local density approximation to the Hohenberg-Kohn density-only functional. Without any fits to solvation data whatsoever, this new method predicts solvation energies of small organic molecules well compared to state-of-the art empirical quantum-chemical cavity approaches. The site interaction potentials produced closely resemble the widely used TIP3P site potentials for water without requiring any empirical parameters.