This work aims to introduce van der Waals forces, and more generally cohesive forces, in a nonsmooth contact dynamics (NSCD) model for studying dense particle systems. The contact dynamics method is based on the relative velocities of interacting bodies. On the other hand, the van der Waals force considers only distance between the bodies. Consequently, we developed a theoretical argument for reconciling velocity and position aspects. As an illustration of our numerical method, we investigated the mixing of different granular species in a rotating drum. We consider large (100 μm radius) and small (5 μm radius) spheres. For these latter, the cohesion forces are larger than their weight. This subject is of great interest in powder handling. We prove that the NSCD approach is suited to modeling dense particle systems such as cohesive powders.