Charge transport in a Hubbard-Holstein junction: Preliminary results from a DFT approach.

Sammanfattning: Many-body systems are extremely complicated to describe due to mutual interactions between the constituent particles. This is for example the case of systems with electron-electron (e-e) and electron-phonon (e-ph) interactions. Here, we consider e-e and e-ph interactions within the Hubbard-Holstein model, a very popular template to describe electron-phonon systems. Specifically, we perform an explorative investigation of the nonequilibrium (transport) properties of a Hubbard-Holstein single impurity coupled to two finite but large noninteracting 1D chains. Such situation is addressed using Density Functional Theory (DFT), where the one-particle density of a many-body interacting system is determined in terms of a non interacting many-particle image system. In more detail, we calculate the electronic density by solving the so-called Kohn-Sham equations, while the central ingredient of the DFT approach, the exchange-correlation potential, is obtained from a reference system using an adiabatic and local density approximation. At the same time, the phonon displacement is evaluated within the Ehrenfest approximation. This two-component (electron+phonon) Kohn-Sham system is time evolved via numerical methods. The conduction properties of the junction are studied as a function of electron-electron and electron-phonon interactions, and of the applied bias. It is found that interactions strongly affect the conductance, mostly in the transient regime, but have relatively small influence on the steady state current. Finally, the current calculated using DFT is also compared to a treatment based on the Ehrenfest approximation. It is found that the latter is a good approximation to the DFT result for large frequencies but not for smaller ones.