Inelastic transport theory from first-principles: methodology and applications for nanoscale devices

摘要

We describe a first-principles method for calculating electronic structure,vibrational modes and frequencies, electron-phonon couplings, and inelasticelectron transport properties of an atomic-scale device bridging two metalliccontacts under nonequilibrium conditions. The method extends thedensity-functional codes SIESTA and TranSIESTA that use atomic basis sets. Theinelastic conductance characteristics are calculated using the nonequilibriumGreen's function formalism, and the electron-phonon interaction is addressedwith perturbation theory up to the level of the self-consistent Bornapproximation. While these calculations often are computationally demanding, weshow how they can be approximated by a simple and efficient lowest orderexpansion. Our method also addresses effects of energy dissipation and localheating of the junction via detailed calculations of the power flow. Wedemonstrate the developed procedures by considering inelastic transport throughatomic gold wires of various lengths, thereby extending the results presentedin [Frederiksen et al., Phys. Rev. Lett. 93, 256601 (2004)]. To illustrate thatthe method applies more generally to molecular devices, we also calculate theinelastic current through different hydrocarbon molecules between goldelectrodes. Both for the wires and the molecules our theory is in quantitativeagreement with experiments, and characterizes the system-specific modeselectivity and local heating.