Time-dependent quantum transport theory from non-equilibrium Green's function approach

Current conserving and gauge invariant conditions are two fundamental requirements for ac quantum transport. These two conditions are satisfied by including the displacement current. Three different approaches can achieve this goal: (1) To consider Coulomb interaction implicitly by partitioning the total displacement current into each leads. (2) To include self-consistent Coulomb interaction explicitly into the Hamiltonian and calculate the conduction current only. (3) To consider the displacement current on the operator level. In this article, we will give a review on these approaches based on non-equilibrium Green's function (NEGF) method. For the first principles atomistic modeling of quantum transport properties, one can carry out the density functional theory (DFT) calculation within the NEGF framework. This NEGF-DFT method has the capability of quantum transport modeling with accurate descriptions of the electronic structure for a wide range of semiconductors, oxides and metals. We will review the current status of this method and its application to molecular junctions in ac regime.