Imposing field boundary conditions in MD simulation of fluids: Optimal particle controller and buffer zone feedback

We formulate a method for imposing continuous field boundary conditions on an MD simulation with little or no disturbance to its dynamics. Our approach combines the previously developed thermodynamic field estimator, which extracts macroscopic fields from particle data, with a novel procedure, optimal in the sense of least disturbance, for imposing prescribed continuum field boundary conditions on the atomistic system. By means of feedback control and assuming molecular chaos in fluids, that disturbance can further be eliminated entirely, thus providing an exact solution for general steady-state fluid problems, where the desired fields at the real boundary is achieved by adjusting actions in a region separated from the real boundary by a buffer zone.