  The quantum tunneling effects between two metallic plates are studied using
the time dependent density functional theory. Results show that the tunneling
is mainly dependent on the separation and the initial local field of the
interstice between plates. The smaller separation and larger local field, the
easier the electrons tunnels through the interstice. Our numerical calculation
shows that when the separation is smaller than 0.6 nm the quantum tunneling
dramatically reduce the enhancing ability of interstice between nanoparticles.
