  We calculate the ion-ion correlation effect on the neutrino-nucleus
scattering in supernova cores, which is an important opacity source for the
neutrinos and plays a vital role in the supernova explosion. In order to
calculate the ion-ion correlation effect we use the results of the improved
hypernetted-chain method calculations of the classical one-component plasma. As
in the preceding studies on this effect, we find a dramatic decrease of the
effective neutrino-nucleus scattering cross section for relatively low energy
neutrinos with E < 20MeV. As a matter of fact, our calculation shows a much
more dramatic reduction of the effective neutrino-nucleus scattering cross
section for the low energy neutrinos with E < 10MeV than the results of
Horowitz. Therefore, the ion-ion correlation effect will be more important than
has hitherto been recognized. We present an accurate analytic fitting formula
that summarizes our numerical results. This fitting formula will facilitate the
application of the present results to the supernova explosion simulations.
