Finite Sphere Coarse-Grained Water Model

This work by FM Bellussi, OM Roscioni, M Ricci, and M Fasano at Politecnico di Torino and MaterialX compares all-atom (AA) water models with their corresponding coarse-grained (CG) representation built using finite-size spheres decorated with virtual charges to account for electrostatic and long-range interactions. This model leads to a quantitative agreement between the physical properties computed at the AA and CG levels. Image 1. shows the cover page of the journal issue.

Image 2. shows the initial guess and an equilibrated sample of coarse-grained water molecules represented as finite-size spheres. The orientation of each sphere is given by the three axes of inertia, shown as blue arrows. The initial guess is a simple cubic grid where all spheres have the same orientation. After thermalisation and equilibration, the spheres are seemingly randomly oriented. However, a short-range order is formed due to the presence of point charges in the coarse-grained model.

Image 3. contains a pictorial view of the (a) All-Atoms and (b) Coarse-Grained water models. The dashed line in (a) represents the Lennard-Jones sphere centred at the oxygen atom. The red circle in (b) represents a finite-size sphere while the white dots represent the virtual charges. Pictorial view of an (c) AA and the equivalent (d) CG sample of bulk water. The arrows in (d) show the orientation of the three axes of inertia per each finite-size sphere representing a single water molecule.