Optimized ladder C and ladder H models for sigma conjugation: chain segmentation in polysilanes

Abstract

Abstract The parameters of the Hückel type ladder C and ladder H models of permethylated oligosilanes have been optimized to reproduce orbital energies obtained from ab initio Hartree–Fock (HF) calculations of 84 conformers with 1–8 silicon atoms at their optimized geometries. With the optimized parameters, the ladder models reproduce the top ∼5% of the ab initio occupied orbital energies with a mean error of 0.03–0.05 eV. Using Koopmans' theorem, trends in the ionization potentials of very long oligosilanes and polysilanes, including their conformational dependence, can now be predicted with the accuracy of the HF/TZ ab initio method. We use the ladder models to examine the chain‐length dependence of conformational effects in chains with up to 40 silicon atoms, with particular attention to the issue of conformationally induced chain segmentation. Copyright © 2002 John Wiley & Sons, Ltd.