  To understand sparse systems we must account for both strong local atom bonds
and weak nonlocal van der Waals forces between atoms separated by empty space.
A fully nonlocal functional form [H. Rydberg, B.I. Lundqvist, D.C. Langreth,
and M. Dion, Phys. Rev. B 62, 6997 (2000)] of density-functional theory (DFT)
is applied here to the layered systems graphite, boron nitride, and molybdenum
sulfide to compute bond lengths, binding energies, and compressibilities. These
key examples show that the DFT with the generalized-gradient approximation does
not apply for calculating properties of sparse matter, while use of the fully
nonlocal version appears to be one way to proceed.
