A BROWNIAN DYNAMICS ALGORITHM FOR CALCULATING THE HYDRODYNAMIC FRICTION AND THE ELECTROSTATIC CAPACITANCE OF AN ARBITRARILY-SHAPED OBJECT

An algorithm originally devised for calculating the diffusion-controll ed reaction rate toward an arbitrarily shaped object is adapted to cal culate the scalar translational hydrodynamic friction and the electros tatic capacitance of the object. In this algorithm Brownian particles are launched from a spherical surface enclosing the object. Each parti cle is propagated until it either hits the enclosed object or crosses the starting surface. In the latter case the particle is allowed to es cape to infinity with an analytically known probability. If the partic le does not escape to infinity, it is ;put-back on the starting surfac e with the correct distribution density and the process is repeated. T he scalar friction or capacitance of the ''probed'' object is proporti onal to the fraction of particles that hit the object. This algorithm is illustrated on a dumbbell made of two equal-size spheres, a cube, a nd a phantom spherical shell having random distributed beads embedded in its surface.