  The adsorption and dissociation of nitrogen molecule on Fe(111) surface is
studied by density functional theory calculations. The simulation results show
that the molecule needs to acquire parallel orientation with respect to the
surface for the adsorption and dissociation. In addition, Fe(111) surface is
more active in dissociating N2 than Fe(100) surface due to its morphology. The
interaction between antibonding molecular orbitals of N2 and partially filled
$3d$ orbitals of Fe atoms on the surface may be the key to the molecular
dissociation of N2. To break down the triple bond of N2, the electron density
on the surface needs to be partially transferred to the molecule to fill the
antibonding molecular orbitals of the nitrogen molecule. The present result may
provide some insights on the dissociation mechanism of molecules over
transition metal surfaces.
