  It has been reported theoretically that the intercalation of nitrogen in the
voids of the rather open cubic structure of bulk Cu3N build up a magnetic
structure. In an extended effort to study this system, we have investigated
spin polarization in bulk and thin films of nitrogen intercalated Cu3N (Cu3N2)
structure by means of first-principles calculations based on Kohn-Sham density
functional theory and ultrasoft pseudopotentials technique. Contrary to the
previous study, the results show that after an accurate structural relaxation
of the system, magnetism in the bulk structure vanishes. This effect is due to
the migration of the intercalated nitrogen atom from the body center of the
cell to the nearness of one of the cell faces. Similar study for the thin films
of 5, 7, 9 and 11 monolayers thickness was performed and it was found that
initial relaxation of structures with 7 and 11 monolayers show a net magnetic
moment of 2.6 {\mu}B. By a more extended survey of the energy surfaces, the
film with 7 monolayers loses its magnetic moment similar to the bulk structure
but the film with 11 monolayers maintains its magnetic moment. It is possibly a
new quantum size effect that keeps the intercalated nitrogen atom of the
middlemost cell at the body center site. Electron density map of this film
clearly confirms the spin polarization upon the intercalated atom.
