double OEGetBondiVdWRadius(unsigned int elemno)
Return the Van der Waals radius for a particular atomic number as
tabulated in A. Bondi, ``Van der Waals Volumes and Radii'', Journal
of Physical Chemistry, Vol. 68, No. 3, pp. 441, 1964. There are
several experimental values for Van der Waals radii (see also
OEGetPaulingVdWRadii) and many additional values used in
molecular mechanics forcefields (including united-atom VdW radii),
so there is often no definitive notion of Van der Waals radius.