Charge relaxation resistance at atomic scale: An ab initio calculation

We report an investigation of ac quantum transport properties of a nanocapacitor from first principles. At low frequencies, the nanocapacitor is characterized by a static electrochemical capacitance C_μ and the charge relaxation resistance R_q . We carry out a first principle calculation within the nonequilibrium Green’s function formalism. In particular, we investigate charge relaxation resistance of a single carbon atom as well as two carbon atoms in a nanocapacitor made of a capped carbon nanotube (CNT) and an alkane chain connected to a bulk Si. The nature of charge relaxation resistance is predicted for this nanocapacitor. Specifically, we find that the charge relaxation resistance shows resonant behavior and it becomes sharper as the distance between plates of nanocapacitor increases. If there is only one transmission channel dominating the charge transport through the nanocapacitor, the charge relaxation resistance R_q is half of resistance quantum h/2e² . This result shows that the theory of charge relaxation resistance applies at atomic scale.