Molecular Surface Area

If we consider the shape of atoms as a sphere where the radius of atoms is equal with the van der Waals's radius then we obtain the van der Waals surface area (VSA) of atoms. In a molecule, the amount of VSA of an atom not contained in other atom's VSA, is considered as available VSA. The sum of available VSA of atoms in a molecule is equal with the molecular VSA.

Solvent molecules are also considered as a sphere which can contact with the molecular VSA. The solvent accessible surface area SASA is equal with the surface area of a molecule that is accessible to a solvent sphere.