  We apply a range of density-functional-theory-based methods capable of
describing van der Waals interactions to weakly bonded layered solids in order
to investigate their accuracy for extended systems. The methods under
investigation are the local density approximation, semi-empirical force fields,
non-local van der Waals density functionals and the random-phase approximation.
We investigate the equilibrium geometries, elastic constants and the binding
energies of a large and diverse set of compounds and arrive at conclusions
about the reliability of the different methods. The study also points to some
directions of further development for the non-local van der Waals density
functionals.
