We have previously reported that the MD method is intrinsically chaotic, and given that we are calculating equilibrium properties, it is a requirement that the dynamics must be mixing (in the language of ergodic theory) . Therefore, we are obliged to use a probabilistic representation in order to control uncertainties . Therefore, we are obliged to use a probabilistic representation in order to control uncertainties . As a result, the distributions of equilibrium properties (such as free energies) obtained from independent MD trajectories differing only in their starting velocities can vary substantially .