Classical molecular dynamics (MD) simulations carried out at fully atomistic resolution are computationally intensive, resulting in limitations in terms of accessible system sizes and time scales. One approach to reduce the computational cost relies on the use of coarse-grained (CG) models, where the resolution of the solute and/or solvent is reduced from individual atoms to beads representative of small atom groups. An early example of this approach is the use of unitedatoms to represent the aliphatic CH n groups as a single interaction site. United-atoms are often employed in models that are otherwise at fully atomistic resolution, and the word fine-grained (FG) will be used here to denote models at (united-)atom resolution.