Polymers and muffin-tin orbitals

A method for calculating electronic properties of polymeric materials is reviewed. It is based on the density-functional formalism of Hohenberg and Kohn. The eigenfunctions to the kohn-Sham equations are expanded in a basis set of linearized muffin-tin orbitals, but no shape approximation for the potential is made. The materials of interest are assumed to be infinite, periodic, noninteracting, helical chains, and the symmetry is explicitly used in constructing helical Bloch waves. As examples of the calculation of structural properties we discuss sulphur helices and the dimerization in trans polyacetylene. A method that allows for calculating energies,of defect-induced orbitals is demonstrated on polarons in polythiophene and solitons in hydrogen fluoride. As an intermediate between insulating and semiconducting polymers we discuss polybutadiene. Momentum densities for different periodic C2H2Cl2 chains are presented, and the importance of including spin-orbit couplings when studying optical properties is demonstrated for bismuth chains. Finally, a method for studying doped chains is presented and preliminary results for the dimerization of a Linear doped carbon chain are reported.