  Using density functional theory, we examine a nitrogen-doped anionic golden
cage (NAu$_{16}^-$). For the exohedral adsorption that is more stable than the
endohedral doping, the bridge and hollow sites have larger binding energies
than the atop sites by ~1 eV. When the N atom is adsorbed on the cage,
electrons are transferred from Au$_{16}^-$ to the N atom. The transition
between the exohedral and endohedral adsorption may occur thermally through a
bridge site. In the infrared active vibrational spectra, exohedral doping
causes greater intensities at higher frequencies than endohedral doping.
