  Embedded density functional theory (e-DFT) is used to describe the electronic
structure of strongly interacting molecular subsystems. We present a general
implementation of the Exact Embedding (EE) method [J. Chem. Phys. 133, 084103
(2010)] to calculate the large contributions of the non-additive kinetic
potential (NAKP) in such applications. Potential energy curves are computed for
the dissociation of Li+-Be, CH3-CF3, and hydrogen-bonded water clusters, and
e-DFT results obtained using the EE method are compared with those obtained
using approximate kinetic energy functionals. In all cases, the EE method
preserves excellent agreement with reference Kohn-Sham calculations, whereas
the approximate functionals lead to qualitative failures in the calculated
energies and equilibrium structures. We also demonstrate an accurate pairwise
approximation to the NAKP that allows for efficient parallelization of the EE
method in large systems; benchmark calculations on molecular crystals reveal
ideal, size-independent scaling of wall-clock time with increasing system size.
