Molecular junctions and molecular motors: Including Coulomb repulsion in electronic friction using nonequilibrium Green's functions

We present a theory of molecular motors based on the Ehrenfest dynamics for nuclear coordinates and the adiabatic limit of the Kadanoff-Baym equations for current-induced forces. Electron-electron interactions can be systematically included through many-body perturbation theory, making the nonequilibrium Green's function formulation suitable for first-principles treatments of realistic junctions. The method is benchmarked against simulations via real-time Kadanoff-Baym equations, finding an excellent agreement. Results on a paradigmatic model of a molecular motor show that correlations can change dramatically the physical scenario by, e.g., introducing a sizable damping in self-sustained van der Pol oscillations.