Density-functional studies of electronic properties of polymers

Abstract

Results of parameter-free electronic-structure calculations on polymers are discussed. The calculations have been performed using various first-principles density-functional methods. Most first-principles studies have been devoted to finite molecules or infinite, periodic chains. Properties of structural defects which break the translational or helical symmetry can therefore most conveniently be studied by mapping the first-principles results on an adequate model Hamiltonian, which subsequently is used in studying the defects. As examples of applications we examine structural properties of sulphur and selenium helices and compare polyethylene and polytetrafiuoroethylene. We then study in detail trans polyacetylene as the prototype of the conjugated polymers and discuss briefly a number of other conjugated polymers. Hydrogen fluoride is investigated as an example of a hydrogen-bonded polymer and some other hydrogen-bonded chains are briefly discussed. We finally mention other systems that have been or can be treated with the current density-functional methods and conclude by discussing their limitations and possible improvements.