Determining the conductivity trends in petroleum-derived molecular electronics using active space methods

Single-molecule electronic devices have long been a topic of intense study due to their unique charge transport characteristics. While most molecular resistors display exponential decay in conductance with increasing molecular length comparable to that of a classical resistor, it has been theorized that a molecular series exists where conductance instead increases with length - a phenomenon known as reverse conductance decay (alternatively anti-ohmic conductance decay). To investigate this effect, we employed Python-based software package our group developed called pyRUQT to perform Non-Equilibrium Green’s Function (NEGF) transport calculations using Multiconfiguration Pair (MCPDFT) and Perdew–Burke–Ernzerhof (PBE) density functional theories. This allows us to compare our NEGF-DFT results to those of no multireference methods in order to quantify the exact role of static correlation in conductance decay reversal. For this study, we examined 2 series of petroleum derivatives to further understand the reverse conductance decay. We found that the reorganization of theoretical active spaces, through the use of complete active space configuration interaction (CASCI) orbitals, improved adherence to known experimental trends with increasing length of the molecular nanowire (>3-4 aromatic rings) notably showing conductance decay reversals.