Sanibel Symposium

In the 1970s Aviram and Ratner proposed creating electronic circuits from single molecules and in the early 2000s advances in single molecule measurement made this possible. However, consistent and accurate theoretical prediction of molecular conductivity is still elusive. Popular theoretical methods, generally based on a combination of non-equilibrium Greens functions and density functional theory, overpredict conductance by an order of magnitude or more and often fail to replicate the Ohmic behavior of the lowvoltage regime. We have developed a new reduced density matrix (RDM) theory for molecular conductivity which employs the variational principle with the current added as an additional condition. Rather than setting the voltage to compute the current, this method allows us to determine the voltage from the reorganization energy of a variational optimization of an RDM to which a specified current is added as a constraint. In a recent paper, we showed that since the RDM theory is able to capture strong correlation, it reproduces experimental values and trends for small aromatic molecules attached to leads with high accuracy. Here, we will discuss its extension to larger systems and potential applications to molecular wires and switches. The current-constrained theory of molecular conductivity will provide a robust way to study the effects of molecular substitution in single molecule junctions.