Force calculation on walls and embedded particles in multiparticle- collision-dynamics simulations

Colloidal solutions posses a wide range of time and length scales so that it is unfeasible to keep track of all of them within a single simulation. As a consequence, some form of coarse graining must be applied. In this work we use the multiparticle collision dynamics scheme. We describe a particular implementation of no-slip boundary conditions upon a solid surface, capable of providing correct forces on the solid bypassing the calculation of the velocity profile or the stress tensor in the fluid near the surface. As an application we measure the friction on a spherical particle when it is placed in a bulk fluid and when it is confined in a slit. We show that the implementation of the no-slip boundary conditions leads to an enhanced Enskog friction, which can be understood analytically. Because of the long-range nature of hydrodynamic interactions, the Stokes friction obtained from the simulations is sensitive of the simulation box size. We address this topic for the slit geometry, showing that the dependence on the system size differs very much from what is expected in a three-dimensional system where periodic boundary conditions are used in all directions.