  We perform density matrix renormalization group (DMRG) calculations
extensively on one-dimensional chains with on site (U) as well as nearest
neighbour (V) Coulomb repulsions. The calculations are carried out in full
parameter space with explicit inclusion of the static bias and we compare the
nature of spin density wave (SDW) and charge density wave (CDW) insulators
under the influence of external electric field. We find that, although the SDW
(U>2V) and CDW (U<2V) insulators enter into a conducting state after a certain
threshold bias, CDW insulators require much higher bias than the SDW insulators
for insulator-metal transition at zero temperature. We also find the CDW-SDW
phase transition on application of external electric field. The bias required
for the transitions in both cases decreases with increase in system size.
