List of RDF descriptors calculated by DRAGON

 

RDF (Radial Distribution Function) descriptors have recently been proposed based on a radial distribution function which can be interpreted as the probability distribution of finding an atom in a spherical volume of radius R. 

The general form of the radial distribution function is represented by:

 

 

where f is a scaling factor (assumed equal to one in the calculations), w are characteristic properties of the atoms i and j, rij is the interatomic distance and nAT is the number of atoms in the molecule [M.C.Hemmer, V.Steinhauer, J.Gasteiger, Vibrat. Spect. 1999, 19, 151-164]. The exponential term contains the interatomic distance rij and the smoothing parameter b (Å–2), which defines the probability distribution of the individual interatomic distance; b can be interpreted as a temperature factor that defines the movement of atoms.

 

RDFRw is generally calculated at a number of discrete points with defined intervals. In DRAGON, a b value equal to 100 Å-2 and a step size for R equal to 0.5 Å are used; therefore, 30 RDF descriptors are calculated for five different weighting schemes: the unweighted case (u), atomic mass (m), the van der Waals volume (v), the Sanderson atomic electronegativity (e) and, the atomic polarizability (p).

 

Besides information about interatomic distances in the entire molecule, the RDF descriptors provide further information, e. g., about bond distances, ring types, planar and non-planar systems and atom types. This fact is a valuable consideration for a computer-assisted code elucidation.