double OEGetBondiVdWRadius(unsigned int elemno)
Returns the Van der Waals radius for a particular atomic number as
tabulated by Bondi [Bondi-1964].
There are several experimental values for Van der Waals radii (see also
OEGetPaulingVdWRadius) 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.