Helical polymers within density functional formalism

Nordita, Blegdamsvej 17, DK 2100 Kobenhavn Ø, Denmark.

Abstract

A method for calculating the electronic ground state properties of a single, infinite, periodic, helical polymer with a straight polymer axis is presented. Here, any material which can be considered as formed by parallel macromolecules interacting only weakly is considered a polymer with these characteristics. The method is based on the density functional formalism in a local approximation and on the Bom-Oppenheimer approximation. The single-particle eigenfunctions are expanded in Linearized Muffin-Tin Orbitals (LMTO's), but the muffin-tin approximation is solely used in defining the basis functions. In the discussion special emphasis is put on the use of symmetry and it is demonstrated that with an atom-centered LMTO basis set of limited size the full symmetry can be used, and that detailed and accurate investigations of general helical polymers thereby can be carried through. Applications of the method to sulphur and selenium helices, carbon disclenide, polysilene, hydrogen fluoride, and sulphur nitride are reported.

Résumé

Une méthode pour calculer les propriétés électroniques de l'état fondamental d'un polymère unique, périodique et hélicoïdal avec un axe polymérique droit est présentée. Elle repose sur le formalisme de la fonctionnelle de la densité avec une approximation locale, l'approximation de Born-Oppenheimer, et l'utilisation d'orbitales muffin-tin linéarisées(LMTO). Des exemples d'application sont discutés.