Dimensionality effects on the electronic and structural properties of PtS2chains

First-principles, density-functional methods are applied to study electroni c and structural properties of infinite, periodic PtS2 chains. Special emph asis is put on identifying those intra- and interchain interactions that ar e responsible for the electronic and the structural properties, respectivel y. Using a single-chain code we first study isolated planar and helical PtS 2 chains. Subsequently, the same method is applied in studying the chains w hen being surrounded by two K counterions per PtS2 unit. Finally, we study the full three-dimensional crystal structure of K2PtS2 both without and wit h the K atoms. The results are compared with experimental information on cr ystalline materials containing PtS2 chains surrounded by K, Na, or Rb count erions. Also the effects of spin-orbit couplings are examined. It is found that the neutral chains have structural properties different from the charg ed ones, but including the K atoms lead to a good agreement with experiment . Despite this, these chains are predicted to be metallic in contrast to ex periment. The calculations on the crystalline compounds show that although the electronic interactions largely are confined to the individual chains, long-range Coulomb interactions change the materials from being metallic in to being semiconducting. Finally, spin-orbit couplings have some effects on the structure and band structures, in particular for the planar conformati on, but do hardly change the calculated structural properties. (C) 1999 Els evier Science B.V. All rights reserved.