One type of surface model is the spacefilling model, which represents atoms as spheres, the radii of which have been chosen to approximate van der Waals contact distance of the respective atom.
Spacefilling models give a good impression of overall molecular size and shape. They are also the simplest surface visualizations, and therefore the fastest for computers to display.
Some surface models require more computing power. a simple van der Waal surface, a smoother representation than the generalized spheres of a spacefilling model. Another common model is the solvent-accessible surface model, which is generated by rolling an imaginary ball with the diameter of a water molecule (1.4 Ã…) over the van der Waals radii used for spacefilling models. The solvent-accessible surface is smoother and larger, especially for proteins, because water cannot fit into narrow crevices or depressions in the surface of protein.