  We present an implicit solvent model for ab initio electronic structure
calculations which is fully self-consistent and is based on direct solution of
the nonhomogeneous Poisson equation. The solute cavity is naturally defined in
terms of an isosurface of the electronic density according to the formula of
Fattebert and Gygi (J. Comp. Chem. 23, 6 (2002)). While this model depends on
only two parameters, we demonstrate that by using appropriate boundary
conditions and dispersion-repulsion contributions, solvation energies obtained
for an extensive test set including neutral and charged molecules show dramatic
improvement compared to existing models. Our approach is implemented in, but
not restricted to, a linear-scaling density functional theory (DFT) framework,
opening the path for self-consistent implicit solvent DFT calculations on
systems of unprecedented size, which we demonstrate with calculations on a
2615-atom protein-ligand complex.
