NO adsorption effects on various functional molecular nanowires

A systematic theoretical study of the electronic structure of metal tape-porphyrin (MTP, M = Ni, Cu, Zn) has been carried out using density functional theory method. The calculations provide a clear elucidation of ground states for the MTPs as well as the adsorption of NO molecule on MTPs. We found that MTPs have small energy gap, which decreases from NiTP to ZnTP. The adsorption of NO on these systems has a minor effect on the geometric structures of MTPs which is attributed to the 3d orbitals of Ni, Cu, and Zn lying lower in energy compared with the Fermi level. This leads to the adsorption of NO on top of the metal atom being a physical adsorption. However, despite the small binding of NO on MTPs, large changes in the electronic properties as well as the magnetic properties of metal tape-porphyrin systems are noted. There is a transition from an insulator to a metal in NiTP and CuTP and an opening of the energy gap in ZnTP. This is due to the small amount of charge transfer from NO molecule to tape-porphyrin, leading to a shift of the Fermi level to a higher energy. Moreover, a change from non-spin polarization to spin polarization is observed in NiTP and ZnTP. The change in magnetization is derived from the unpaired electron in π* orbital of NO molecule.