  Monatomic and molecular hydrogen and also oxygen, as well as water molecules
and OH that are exposed to atomic copper in intimate contact have been studied
theoretically using computational methods. The authors optimized moderately
large structures of Cu/H/Cu, Cu/HCuH/Cu, Cu/H$_2$/Cu, Cu/H$_2$O/Cu, Cu/OH/Cu,
Cu/O/Cu, Cu/O$_2$/Cu, and calculated appropriate values for conductance and
inelastic tunneling spectroscopy (IETS) properties of the contact junctions;
elucidating them as being a possible outcome resulting from the exposure of
copper electrodes to the atomic/molecular contaminant species. Here we also
demonstrate the IETS properties, by means of ab-initio calculations, that can
determine the form of the junction geometries. Furthermore, we identify the
bonding geometries at the interfaces of the copper electrodes that directly
give rise to the specific IETS signatures that have been observed in recent
experiments. Based on low-bias conductance and IETS calculations, for the
specific case of water exposure of copper electrodes, it was concluded that a
single hydrogen or a single oxygen atom bridging the copper electrodes is not
responsible for the high conductance peak measurements. Regarding Model 4,
where an individual water molecule is considered to be the bridging
constituent, our computational results suggest that it has a relatively low
probability of being an appropriate candidate. Based upon current computational
results, the two hydrogens in Model 3 appear to be in molecular form, although
they still form a bond with the adjacent copper atoms. Comparing computational
with experimental results indicates that Model 3 is in acceptable agreement
with available data.
