In recent years, first-principle electronic structure calculations have been carried out to investigate such diverse phenomena as charge transport in molecular wires, optical properties of quantum structures and in photonics. However, at this time the prohibitive computational cost does not allow for such calculations to be easily carried out on nano-scale device structures comprising thousands of atoms. In addition, there are issues relating to the applicability of these approaches to describing the excitations that ought to be involved in charge transport.
Self-consistent extended Huckel theory (SC-EHT) has proved very effective in describing the band alignment at semiconductor interfaces, and optical properties of partially covered surfaces, as well as being employed in studying the electronic states of large molecules. We have developed a non-equilibrium Greens function (NEGF) SC-EHT code that may be applied to study charge transport through molecular wires. We study the transmission of a porphyrin molecule attached via thiol linkers to gold electrodes, compare our results with those obtained from density functional theory (DFT). We have studied the influence the thiol position on the Au substrate has on the conduction and the dependence of the electron transmission on the molecular conformation. In addition, we also report on the results of some preliminary investigations studying the influence of water on the conduction pathways.