The LDA and GGA functionals correspond to the first term of the expansion in eqn (26). Examples of the second-order term ("two-point functionals") are the naive Hartree energy and the vdW-DF energy functional of Langreth, Lundqvist, and coworkers. The expansion in eqn ( ) may be relevant in the quest for explicit density functionals for the kinetic energy, a topic that has seen revived interest recently in the context of orbital-free DFT. Here, however, I will confine my remarks to the theory of vander-Waals interactions (London dispersion), 396 with which I am more familiar.