  We investigate the Peierls transition in the one-dimensional Peierls-Hubbard
model at half filling in the adiabatic approximation for the lattice. Depending
on the value of the electron-lattice coupling constant g the equilibrium
dimerization can be either enhanced or suppressed by the Hubbard interaction U.
Applying second order perturbation theory we determine the critical value g_c =
0.689348 below which the Hubbard interaction enhances the dimerization.

Strongly Correlated Electrons