These are molecular descriptors defined as the amount of van der Waals surface area (VSA) having a property P in a certain range [P.Labute, J. Mol. Graph. Model. 2000, 18, 464-477]. To generate P_VSA-like descriptors, first, the van der Waals surface area VSAi of each atom is estimated according to the following:
where R is the atomic van der Waals radius, the summation goes over all the atoms (nAT), but accounts only for contributions from atoms bonded to the ith atom, αij being the elements of the adjacency matrix. The quantity gij is calculated as:
where the term bij is the ideal length of the bond formed by atoms i and j, calculated according to the formula:
where rij is a reference bond length and cij a correction term depending on the bond multiplicity: 0 for single bond, 0.1 for aromatic, 0.2 for double, and 0.3 for triple bonds.
Van der Waals radii (in Angstrom) used for P_VSA-like descriptors
Reference bond lengths (in Angstrom) used for P_VSA-like descriptors.