SPIN CONTAMINATION, DISORDER EFFECTS, AND SOLITON DYNAMICS IN THE PARISER-PARR-POPLE MODEL OF TRANSPOLYACETYLENE

Numerical calculations on the interactions of solitons with impurities in trans-polyacetylene are described. For this purpose the Pariser-Parr-Pople Hamiltonian in mean-field form is used. To remove spin contaminations inherent in the unrestricted Hartree-Fock-Slater determinant, the major contaminating component is annihilated in each self-consistent-field iteration cycle (annihilated unrestricted Hartree-Fock method). As impurities a conjugation break (e.g., a CH2 group instead of CH) and isoelectronic chemical substitutions (B,N,NH+, O+) for CH are considered. Further, a random sequence in all parameters along the chain is introduced. Such a random sequence is probably present in the system due to its disordered structure. It is shown that for reasonable disorder strength the soliton is able to move through the chain.