Local-Density Functional Electronic Structure of Helical Chain Polymers

Abstract

Polymers represent an area of chemistry intermediate between molecular chemistry and solid-state physics. The one-dimensional periodicity leads to delocalization of electron states analogous to that in crystals, but the finiteness in other dimensions requires the use of localized wavefunctions as in molecular approaches. Although ab initio methods have been used to calculate both total energies and electronic structures of chain polymers for several decades (Del Re, et al., 1967; André, 1969), the ability to calculate accurate total energies for polymers (or even large molecular clusters) within a local-density functional (LDF) approach has come about principally within the last decade. Our group at the Naval Research Laboratory has had great success in recent years in applying local-density functional methods to this area of chemistry, in particular to polyacetylene (Mintmire and White, 1983abcd, 1987ab) and polysilane systems (Mintmire, 1989ab), using methods developed for polymer chains with translational symmetry, as well as the calculation of electronic properties on molecular species (Kutzler, et al., 1986; White, et al., 1986; Mintmire, et al., 1987). The techniques for polymers are based on one-electron wavefunctions constructed from linear combinations of Gaussian-type orbitale (LCGTO), using algorithms equivalent to an infinite chain limit of the molecular scheme introduced by Dunlap, et al. (1979ab).