Electronic and structural properties of extended-chain compounds and polymers

Results of density functional calculations on infinite, periodic chains are reported. The method that is applied is based on linearized muffin-tin orb itals as basis functions, although the full potential and not only its muff in-tin part is included in the calculations. Special emphasis is put on ana lyzing the interatomic interactions by means of crystal-orbital overlap or Hamilton populations (COOP and COHP, respectively). As examples of conjugat ed polymers, hans-polyacetylene and polycarbonitrile are studied. Hero, in particular, the existence of a bond length alternation is discussed. Subseq uently, PtS2 (both without and with K counterions) and NbSe3 chains are con sidered. For the former, the single-chain calculations are supplemented wit h calculations on the crystalline compounds, and it is shown how single-cha in effects are responsible for the structural properties whereas interchain effects have to be included in order to account for all the electronic pro perties. Parts of the results are explained through an analysis of the COOP and COHP. For NbSe3 the three different structures occurring in the crysta lline material are considered, and the implications of our results for the existence of charge density waves as well as the importance of spin-orbit c ouplings are discussed. Finally, HF as an example of an extended hydrogen-b onded system is examined, and it is demonstrated how the electronic interac tions change when the covalent and hydrogen bonds are interchanged as it oc curs in charge transport via solitons. (C) 2000 John Wiley & Sons, Inc.