In the mixed-resolution variant, the FG and CG molecules are allowed to mix in the buffer layer. The extent of mixing is typically controlled by means of attractive and/or repulsive restraints relative to the solute. In the adaptive-resolution variant, the FG and CG particles interconvert into each other as they cross the buffer layer. When N G is one, this can be achieved by morphing, i.e. interpolating between the interaction potentials or forces of the FG and CG models using a coupling variable that varies continuously with the position across the buffer layer. When N G > 1, the transformation maps unequal numbers of molecules, and may be combined with a bundling scheme that associates clusters of nearby FG molecules to a single CG bead. The most popular adaptive-resolution schemes relying on morphing across a fixed buffer layer are the Adaptive Resolution Simulation (AdResS) scheme and its Hamiltonian (H-AdResS) variant (see also Refs. 16,70-77 for related approaches). Here, the buffer region is defined by an internal (FG to buffer) and an external (buffer to CG) boundary, both of which are fixed in space relative to the solute. Between the two boundaries, the resolution of a solvent particle changes progressively according to a switching parameter λ that is a continuous function of position, and evaluates to 1 (full FG) and to 0 (full CG) at the inner and outer boundaries, respectively. The switching is applied to the forces in AdResS (thereby enforcing the validity of Newton's third law) or to the Hamiltonian in H-AdResS (thereby enforcing the conservation of the total energy).