Simple and accurate method for time-dependent transport along nanoscale junctions

A simple method that accurately captures the dynamics of metal–molecule–metal junctions under the influence of time-dependent driving forces is presented. In the method, the metallic contacts are modeled explicitly as a discrete set of levels that are dynamically broadened via an artificial damping term in the equations of motion. The approximations that underlie the method are revealed via a derivation of the effective equations of motion within the framework of nonequilibrium Green’s functions (NEGF) theory. As shown, the method applies to junctions that can be described by an effective independent Fermion Hamiltonian, admits arbitrary time dependence in the molecular Hamiltonian, and is restricted to time-dependent voltages that are adiabatically slow. The method is trivial to implement computationally, has a well-defined range where the results are independent of artificial model parameters, and is numerically shown to quantitatively reproduce the time-dependent transport characteristics of a model mo...