  The nonlocal correlation energy in the van der Waals density functional
(vdW-DF) method [Phys. Rev. Lett. 92, 246401 (2004); Phys. Rev. B 76, 125112
(2007); Phys. Rev. B 89, 035412 (2014)] can be interpreted in terms of a
coupling of zero-point energies of characteristic modes of semilocal
exchange-correlation (xc) holes. These xc holes reflect the internal functional
in the framework of the vdW-DF method [Phys. Rev. B 82, 081101(2010)]. We
explore the internal xc hole components, showing that they share properties
with those of the generalized-gradient approximation. We use these results to
illustrate the nonlocality in the vdW-DF description and analyze the vdW-DF
formulation of nonlocal correlation.
