Nonlocal van der Waals functionals for solids: Choosing an appropriate one

The nonlocal van der Waals (NL-vdW) functionals [M. Dion et al., Phys. Rev. Lett. 92, 246401 (2004)] are being applied more and more frequently in solid-state physics, since they have shown to be much more reliable than the traditional semilocal functionals for systems in which weak interactions play a major role. However, a certain number of NL-vdW functionals have been proposed during the last few years, such that it is not always clear which one should be used. In this work, an assessment of NL-vdW functionals is presented. Our test set consists of weakly bound solids, namely rare gases, layered systems such as graphite, and molecular solids, but also strongly bound solids in order to provide a more general conclusion about the accuracy of NL-vdW functionals for extended systems. We found that among the tested functionals, rev-vdW-DF2 [I. Hamada, Phys. Rev. 13 89, 121103(R) (2014)] is very accurate for weakly bound solids, but also quite reliable for strongly bound solids.