Finite-size correction for the diffusion front roughness exponent

The width of the diffusion front originated by the random motion of particles under a concentration gradient is evaluated by means of Monte Carlo simulations. It is found that the roughness exponent of the front exhibits a systematic dependence on the sample size that can be rationalized in terms of a finite-size correction. Extrapolation to the thermodynamic limit allows us to evaluate the actual roughness exponent in excellent agreement with theoretical predictions linking the diffusion system to the percolation problem.