A geometrical method for the Smoluchowski equation on the sphere

A study of the diffusion of a passive Brownian particle on the surface of a sphere and subject to the effects of an external potential, coupled linearly to the probability density of the particle's position, is presented through a numerical algorithm devised to simulate the trajectories of an ensemble of Brownian particles. The algorithm is based on elementary geometry and practically only algebraic operations are used, this makes the algorithm efficient and simple, and converges, in the \textit{weak sense}, to the solutions of the Smoluchowski equation on the sphere. Our findings show that the global effects of curvature are taken into account in both, the time dependent and stationary processes.