  The persistent current in three-dimensional mesoscopic rings is investigated
numerically. The model is tight-binding one with random site-energies and
interaction between electrons. The Hartree-Fock approximation is adopted for
the interaction between electrons, and models with up to $3\times 4\times 40$
sites are investigated. It is shown that the long-range Coulomb interaction
enhances the persistent current considerably for rings with finite width. It is
also shown that long-rangedness of the interaction is essential for the
enhancement. Screening of the random site-energy is attributed to this
enhancement.
