APPLICATION OF THE ELONGATION METHOD TO THE CALCULATION OF ELECTRONIC-STRUCTURES OF THE INTERFACE AND THE LOCAL DEFECT STATES IN A POLYMER - AN ANALYSIS OF THE PERIODICITY IN THE ELECTRONIC STATES OF A NONPERIODIC POLYMER BY USING THE CLUSTER-SERIES CALCULATION

We have developed an approach at the Hartree-Fock level by which it is possible to calculate the electronic structures of large polymers wit h or without periodic sequences systematically. This elongation method is based on the concept of a cluster-series calculation which means t he successive connection of cluster molecules at the molecular orbital level in approximating a large polymer as a cluster molecule. It has already been reported that we can extract the periodic condition of th e electronic states within the series of extended clusters by using th e cluster-series model. Recently, we tried to introduce the elongation method into the program package of semiempirical molecular orbital me thods MOPAC. In the present paper, we report results of applications t o the calculations of three polymer systems by using AM1 parameters, t hat is, the first system is the periodic polymer, the second is the in terface between two blocks in a polymer chain, and the third is the lo cal defect within a periodic polymer. In calculations of periodic poly mers, clusters of polyethylene, polytetrafluoroethylene, polyacetylene , or polydifluoroacetylene were elongated in one direction, and the in terfaces between the above polymer blocks with ethylene- or acetylene- type chain were dealt with by the two-directional elongation method. A lso, the solitonic structures with one plus or minus charge within pol yacetylene chain were created in elongation calculations of the bidire ctional extension as models for the local defect in a periodic polymer . Moreover, we discussed periodic states of electronic structures in t hese systems from cluster-series calculations.