Joint density-functional theory for electronic structure of solvated systems

We introduce a form of density-functional theory for the ab initio description of electronic systems in contact with a molecular liquid environment. This theory rigorously joins an electron density functional for the electrons of a solute with a classical density-functional theory for the liquid into a single variational principle for the free energy of the combined system. We then present an approximate functional in which orientational ordering appears only through a simple model dielectric response. Even with the shortcomings of this preliminary functional, the resulting theory predicts, without any fitting of parameters to solvation data, solvation energies as well as state-of-the-art quantum-chemical cavity approaches, which do require such fitting. Future work should focus on including orientational ordering in the joint density functional.