  We present an explicit and simple approximation for the superadiabatic excess
(over ideal gas) free power functional, admitting the study of the
nonequilibrium dynamics of overdamped Brownian many-body systems. The
functional depends on the local velocity gradient and is systematically
obtained from treating the microscopic stress distribution as a conjugate
field. The resulting superadiabatic forces are beyond dynamical density
functional theory and are of viscous nature. Their high accuracy is
demonstrated by comparison to simulation results.
