Particle tracing in RF module

Hello everyone:
I want to trace a particle in the optical gradient field(In the RF module I have get the magnitude of the optical force). The optical force drag the particle into the center of the optical field.
BUT now I must consider the Brownian motion exerted on the particle.
I want to know how to take it(Brownian motion) into considerration?
Can I use the particle tracing module?

THANKS!