 COSMO treats each solvent as a continuum with a permittivity "ε" and therefore belongs to the "continuum solvation" group of models.As in all these models COSMO approximates the solvent by a dielectric continuum, surrounding the solute molecules outside of a molecular cavity.In most cases it is constructed as an assembly of atom-centered spheres with radii approximately 20% larger than the Van der Waals radius.