RESONATING HARTREE-FOCK STUDIES ON ELECTRON CORRELATION AND BOND ALTERNATION IN THE ONE-DIMENSIONAL HALF-FILLED HUBBARD-MODEL

Effects of the on-site electron-electron Coulomb interaction U on bond alternation in the one dimensional half filled Hubbard model are stud ied by the resonating Hartree-Fock method. Two kinds of SDW neutral so litons S(A)0 and S(B)0 exist in a bond alternated lattice which are ce ntered at a long bond and a short bond, respectively. S(A)0 enhances b ut S(B)0 suppresses the alternating bond order (ABO) due to bond alter nation. Quantum fluctuations in the ground state involve more S(A)0's than S(B)0's because the former has lower energy than the latter with increasing bond alternation so that they enhance the ABO in the true g round state and consequently the bond alternation. The spin and single t pair correlation functions show that electrons tend to make singlet pairs on nearest neighbor short bonds even from small U's and small bo nd alternations.