We show that when a molecular junction is under an external bias, its properties cannot be uniquely determined by the total electron density in the same manner as the density functional theory for ground state properties. In order to correctly incorporate bias-induced nonequilibrium effects, we present a dual mean field ({DMF)} approach. The key idea is that the total electron density together with the density of current-carrying electrons are sufficient to determine the properties of the system. Two mean fields, one for current-carrying electrons and the other one for equilibrium electrons can then be derived. Calculations for a graphene nanoribbon junction show that compared with the commonly used ab initio transport theory, the {DMF} approach could significantly reduce the electric current at low biases due to the non-equilibrium corrections to the mean field potential in the scattering region.

}, keywords = {Ab initio calculations, Chemical potential, Density functional theory, Electric currents, Electron scattering, Hohenberg Kohn theorem, Mean field theory, Molecular electronic properties, Quantum transport, Transport properties}, issn = {0021-9606, 1089-7690}, doi = {10.1063/1.4833677}, url = {http://scitation.aip.org/content/aip/journal/jcp/139/19/10.1063/1.4833677}, author = {Liu, Shuanglong and Feng, Yuan Ping and Zhang, Chun} }