Martini 3 CG model of caffeine. (a) The 14 non-hydrogen atoms are described by a 7 T-bead model; the indices used for the beads in the CG topology file are also shown. (b) Rendering of the CG model: apolar aromatic and intermediately polar beads are displayed in silver (TC5, TN1) and blue (TN5a) while polar (TP1a) beads are in red. As described in Sec. 2.5 and shown in the rendering, beads 1, 3, 6, and 7 are connected via constraints and form a “hinge” construction, while beads 2, 4, and 5 are constructed as virtual sites. (c) Representative bond and dihedral distributions: OPLS is in blue while Martini is in red. Note that while distance 3-6 corresponds to an actual constraint at the CG level, distances 5-6 and 1-2 at the CG-level result from the virtual site constructions. (d) A comparison of the Connolly surfaces of the AA (gray) and Martini 3 (blue) models; the inset shows a side view of the molecule.