Density matrix renormalization group study of dimerization of the Pariser-Parr-Pople model of polyacetilene

We apply the density matrix renormalization group method to the Pariser-Par r-Pople Hamiltonian and investigate the onset of dimerization. We deduce th e parameters of the hopping term and the contribution of the sigma bonds fr om ab initio calculations on ethylene. Denoting by R-ij the C-C distances, we perform a variational optimization of the dimerization delta=(R-i,R-i+1- R-i-1,R-i)/2 and of the average bond length Ro for chains up to N = 50 site s. The critical value of N at which the transition occurs is found to be be tween N = 14 and N = 18 for the present model. The asymptotic values for la rge N for R-0 and delta are given by 1.408(3) Angstrom and 0.036(0) Angstro m. (C) 1999 American Institute of Physics. [S0021-9606(99)31001-1].