  We review the screening nature and many-body physics foundation of the van
der Waals density functional (vdW-DF) method, a systematic approach to
construct truly nonlocal exchange-correlation energy density functionals. To
that end we define and focus on a class of consistent vdW-DF versions that
adhere to the Lindhard screening logic of the full method formulation. The
consistent-exchange vdW-DF-cx version and its spin extension represent the
first examples of this class; In general, consistent vdW-DFs reflect a
concerted expansion of a formal recast of the adiabatic-connection formula, an
exponential summation of contributions to the local-field response, and the
Dyson equation. We argue that the screening emphasis is essential because the
exchange-correlation energy reflects an effective electrodynamics set by a
long-range interaction. Two consequences are that 1) there are, in principle,
no wiggle room in how one balances exchange and correlation, for example, in
vdW-DF-cx, and that 2) consistent vdW-DFs have a formal structure that allows
them to incorporate vertex-correction effects, at least in the case of levels
that experience recoil-less interactions (for example, near the Fermi surface).
We explore the extent to which the strictly nonempirical vdW-DF-cx formulation
can serve as a systematic extension of the constraint-based semilocal
functionals. For validation, we provide a complete survey of vdW-DF-cx
performance for broad molecular processes and comparing to the
quantum-chemistry calculations that are summarized in that paper. We also
provide new vdW-DF-cx results for metal surface energies and work functions
that we compare to experiment. Finally, we use the screening insight to
separate the vdW-DF nonlocal-correlation term and present tools to compute and
map the binding signatures.
