the number of crystal structures that have both the central and contact groups present.
Nc
:
the number of crystal structures in which the central group and contact group form a contact with distance (R) less than the sum of van der Waals radii (V).
drel
:
relative density, is defined as drel = dshort/dlong, where dshort is the density of contact groups with R<V, and dlong is the density of contact groups with V<R<V+0.5.
