double OEGetPaulingVdWRadius(unsigned int elemno)
Returns the Van der Waals radius for a particular atomic number as
tabulated by Linus Pauling [Pauling-1960].
There are several experimental values for Van der Waals radii (see also
OEGetBondiVdWRadius) 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.