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-controlled reaction rate toward an arbitrarily shaped object is adapted to calculate the scalar translational hydrodynamic friction and the electrostatic capacitance of the object. In this algorithm Brownian particles are launched from a spherical surface enclosing the object. Each particle is propagated until it either hits the enclosed object or crosses the starting surface. In the latter case the particle is allowed to escape to infinity with an analytically known probability. If the particle does not escape to infinity, it is ;put-back on the starting surface with the correct distribution density and the process is repeated. The scalar friction or capacitance of the ''probed'' object is proportional to the fraction of particles that hit the object. This algorithm is illustrated on a dumbbell made of two equal-size spheres, a cube, and a phantom spherical shell having random distributed beads embedded in its surface.