  A possible ground state of NaV_2O_5 is proposed based on the Hartree
approximation for both on-site and intersite Coulomb interactions. The results
indicate that the intersite Coulomb interaction induces a zigzag type of charge
disproportionation (i.e. charge ordering) along the ladders of V-ions resulting
in the localized spins between neighboring ladders to form a spin gap. This new
state, which is different from the spin-Peierls state so far believed, seems to
be consistent with the existing experimental results.
