Charge on the quantum dot in the presence of tunneling current

The calculation of the charge present in central region of the double barrier structure at nonequilibrium conditions is discussed. We propose here a simple method to calculate nonequilibrium Greenʹs functions which allows consistent calculations of retarded and distribution functions. To illustrate the approach, we calculate the charge on the quantum dot coupled via tunnel barriers to two external leads having different chemical potentials μL and μR. The obtained results have been compared with other approaches existing in the literature. They all agree in the equilibrium situation and the departures grow with increasing the difference μL−μR.