Electronic transport properties of molecular devices

Density functional theory calculations combined with non-equilibrium Greenʹs function technique have been used to compute electronic transport in organic molecules. In our approach the system Hamiltonian is obtained by means of a self-consistent density-functional tight-binding (DFTB) method. This approach allows a first-principle treatment of systems comprising a large number of atoms. The implementation of the non-equilibrium Greenʹs function technique on the DFTB code allows us to perform computations of the electronic transport properties of organic and inorganic molecular-scale devices. The non-equilibrium Greenʹs functions are used to compute the electronic density self-consistently with the open-boundary conditions naturally encountered in transport problems and the boundary conditions imposed by the potentials at the contacts. The Hartree potential of the density-functional Hamiltonian is obtained by solving the three-dimensional Poissonʹs equation involving the non-equilibrium charge density. The method has been applied to study the transport properties of a variety of molecular systems. It also allows for self-consistent computations of the atomic forces and to perform molecular dynamics simulations which are used to investigate the role of thermal fluctuations in coherent transport through organic molecules.