  Modeling nanoscale capacitance presents particular challenge because of
dynamic contribution from electrodes, which can usually be neglected in
modeling macroscopic capacitance and nanoscale conductance. We present a model
to calculate capacitances of nano-gap configurations and define effective
capacitances of nanoscale structures. The model is implemented by using a
classical atomic charge-dipole approximation and applied to calculate
capacitance of a carbon nanotube nano-gap and effective capacitance of a
buckyball inside the nano-gap. Our results show that capacitance of the carbon
nanotube nano-gap increases with length of electrodes which demonstrates the
important roles played by the electrodes in dynamic properties of nanoscale
circuits.
