Conductance of a Single Magnesium Porphine Molecule on an Insulating Surface

Using first-principles calculations based on density functional theory and nonequilibrium Green’s function formalism, we study the electron transport through a magnesium porphine molecule adsorbed on an ultrathin NaCl bilayer. The conductance of the tip–vacuum–molecule–NaCl–metal junction depends on the orientation of the molecule on the insulating surface and the tip position above the molecule, which is mediated largely by the molecular pz orbital. The movement of molecule results in a perturbation to the spatial extension of these orbitals, leading to different conductions.