This model was updated by Lian and Yalkowsky to include two more descriptors for entropy of melting in the Unified Physiochemical Property Estimation Relationships (UP-PER) method. These additional descriptors are 1) aromatic eccentricity -the number of atoms in aromatic rings, and 2) aliphatic eccentricity -the number of atoms in aliphatic (non-aromatic) rings. These terms capture the tendency of flat or elongated molecules to be partially ordered in the liquid phase (which decreases the change in entropy between the solid and liquid phase, thus decreasing the entropy of melting). Thus, the final form of the equation we use to model the entropy of melting is: