Charge and spin transport in porphyrin-based molecular junctions

We study weak-bias charge and spin transport behavior of four metal-porphyrin molecules in molecular junctions, using a combination of break-junction experiments and a self-energy corrected first-principles approach based on density functional theory. Some of the molecules are open-shell, and they are of potential interest to spin filtering and solar energy conversion. Optimally-tuned range-separated hybrid functionals are used in combination with a correction for static polarization effects to yield accurate level alignment between Fermi level and dominating conducting orbital energies in the junction. We find that the conductance can change by up to a factor of two when different metal cations are used. Our calculations of low-bias conductance generate similar trends and are in quantitative agreement with experimental measurements. Implications for spin transport are discussed.