Electronic structures of large, extended, nonperiodic systems by using the elongation method: Model calculations for the cluster series of a polymer and the molecular stacking on a surface

The elongation method based on the molecular orbital (MO) theory, which enables us to extend a polymer with any molecular fragments theoretically, has recently been developed by our group. As the next step, we introduced an approach based on the crystal orbital (CO) theory into above treatment. In the present work, the elongation method was developed at the Hartree–Fock level with CNDO/2 parameters and applied to model systems composed of the cluster series of a polymer and the molecular stacking on a surface. In the cluster‐series calculations, the hydrogen molecule [(H₂)_n], hydrogen fluoride [(HF)_n], polyethylene, and polyacetylene were created successively to approximate their one‐dimensional periodic polymers by using the MO‐based elongation method. In the molecular‐stacking models, we described the hypothetical surface of crystal as periodically arranged hydrogen molecules by the COs, and several hydrogen molecules were stacked up on the surface one after another with the elongation procedure. Furthermore, the lattice defect on surface in which a part of stacked layer is lacking was dealt with by our approach. We also treated carbon monoxide chemisorption on a periodic magnesium chain as a more realistic model. Results for these systems support the applicability of our method for nonperiodic interactions in one‐ and two‐dimensional large systems. © 1995 John Wiley & Sons, Inc.