  Quantum-chemical processes in liquid environments impact broad areas of
science, from molecular biology to geology to electrochemistry. While
density-functional theory (DFT) has enabled efficient quantum-mechanical
calculations which profoundly impact understanding of atomic-scale phenomena,
realistic description of the liquid remains a challenge. Here, we present an
approach based on joint density-functional theory (JDFT) which addresses this
challenge by leveraging the DFT approach not only for the quantum mechanics of
the electrons in a solute, but also simultaneously for the statistical
mechanics of the molecules in a surrounding equilibrium liquid solvent.
Specifically, we develop a new universal description for the interaction of
electrons with an arbitrary liquid, providing the missing link to finally
transform JDFT into a practical tool for the realistic description of chemical
processes in solution. This approach predicts accurate solvation free energies
and surrounding atomic-scale liquid structure for molecules and surfaces in
multiple solvents without refitting, all at a fraction of the computational
cost of methods of comparable detail and accuracy. To demonstrate the potential
impact of this method, we determine the structure of the solid/liquid
interface, offering compelling agreement with more accurate (but much more
computationally intensive) theories and with X-ray reflectivity measurements.
