In equilibrium, it is assumed that the flux goes to zero. Therefore, Boltzmann statistics can be applied for the probability of a particles location at equilibrium, where F ( r ) = − − ∇ ∇ U ( r ) is a conservative force and the probability of a particle being in a state r is given as P ( r , t | r 0 , t 0 ) = e − − β β U ( r ) Z .