  Using time-dependent density-matrix renormalization group, we study the time
evolution of electronic wave packets in the one-dimensional extended Hubbard
model with on-site and nearest neighbor repulsion, U and V, respectively. As
expected, the wave packets separate into spin-only and charge-only excitations
(spin-charge separation). Charge and spin velocities exhibit non-monotonic
dependence on V. For small and intermediate values of V, both velocities
increase with V. However, the charge velocity exhibits a stronger dependence
than that of the spin, leading to a more pronounced spin-charge separation.
Charge fractionalization, on the other hand, is weakly affected by V. The
results are explained in terms of Luttinger liquid theory in the weak-coupling
limit, and an effective model in the strong-coupling regime.
