  We discuss the calculation of the double occupancy using Dynamical Mean-Field
Theory (DMFT) in finite dimensions. The double occupancy can be determined from
the susceptibility of the auxiliary impurity model or from the lattice
susceptibility. The former method underestimates, whereas the latter
overestimates the double occupancy. We illustrate this for the square-lattice
Hubbard model. We propose an approach for which both methods lead to identical
results by construction and which resolves this ambiguity. This self-consistent
dual boson scheme results in a double occupancy that is numerically close to
benchmarks available in the literature.
