STUDIES ON THE STRUCTURAL UNIT AND SUSPENDING TERMINAL GROUPS IN THE QUASI-ONE-DIMENSIONAL PERIODIC SYSTEM

Quasi-one-dimensional periodic systems were investigated by the new pr oposed extrapolation method. The effect of the selection of the differ ent structural units and their spin states on the periodic system was also studied. A quantum chemical calculation investigation of a 28 qua si-one-dimensional periodic system with MNDO (UHF) and EHMO/ASED-EHCO/ ASED was undertaken. Quantum chemical calculation results with the MND O (UHF) method showed that the proposed new method could be applied in the situation of the more precise semiempirical method. The selection of the different structural units and their spin states do not affect the extrapolated structural unit energy. The energy of suspending ter minal group is generally higher for those with a higher bond order. Th e interaction energy between the suspending terminal groups generally decreases with the chain length. Comparison between the extrapolation results of EHMO/ASED and those from the crystal orbital calculation of EHCO/ASED indicates their equivalence, thus confirming the validity o f the proposed method. (C) 1995 John Wiley & Sons, Inc.