Consider the orthorhombic, periodic simulation box in Fig. , where the blue circles represent molecules (either solvent or solute). VSS-RNEMD is a simulation method which imposes an unphysical momentum flux, j z (p x ), between the box's orange and yellow regions. This momentum flux is functionally equivalent to a shear stress, τ zx on the system. For most fluids, Newton's law connects the shear stress to the shear viscosity,