Density-functional theory of nonequilibrium tunneling

Nanoscale optoelectronics and molecular-electronics systems operate with current injection and nonequilibrium tunneling---phenomena that challenge consistent descriptions of the steady-state transport. The current affects the electron-density variation and hence the intermolecular and intramolecular bondings which in turn determine the transport magnitude. The standard approach for efficient characterization of steady-state tunneling combines ground-state density-functional theory (DFT) calculations (of an effective scattering potential) with a Landauer-type formalism and ignores all actual many-body scattering. The standard method also lacks a formal variational basis. This paper formulates a Lippmann-Schwinger (LS) collision density-functional theory (LSC DFT) for tunneling transport with full electron-electron interactions. Quantum-kinetic (Dyson) equations are used for an exact reformulation that expresses the variational noninteracting and interacting many-body scattering T matrices in terms of universal density functionals. The many-body LS variational principle defines an implicit equation for the exact nonequilibrium density.