It has been known for some time that widely-spaced lowdimensional metals have van-der-Waals interactions that are qualitatively different from those between nonmetallic structures with a similar geometry; 398-400 for some discussion, see Chapter 11 of ref. 396. Recently, it has been found that this specific metal-lic van-der-Waals physics is important beyond the asymptotic region, indeed right down to contact, for metallic nanotubes and doped graphene sheets. This behaviour was captured by calculations 401 of the electron correlation energy in direct RPA (dRPA). Methods like dRPA start from an electronic band-structure calculation and are thereby sensitive to the presence or absence of a zero HOMO-LUMO gap (band gap). I fear that a very high order in the functional expansion in eqn ( ) might be needed to capture such physics. I wonder, though, whether one could use a close examination of the ground-state electron density in the tunnelling region between atoms, in order to recognize the band gap. Certainly, this region determines the overlap (tunnelling) energy integral t in the tight-binding description of electronic band structure. In that case, perhaps the first few terms on the right-hand side of eqn ( ) might be sufficient.