  The density-matrix renormalization group is used to study the phase diagram
of the one-dimensional half-filled Hubbard model with on-site (U) and
nearest-neighbor (V) repulsion, and hopping t. A critical line V_c(U)
approximately equal to U/2 separates a Mott insulating phase from a
charge-density-wave phase. The formation of bound charge excitations for V > 2t
changes the phase transition from continuous to first order at a tricritical
point U_t = 3.7t, V_t=2t. A frustrating effective antiferromagnetic spin
coupling induces a bond-order-wave phase on the critical line V_c(U) for U_t <
U < 7-8 t.
