Abstract :
First-principles, density-functional methods are applied to study electronic and structural properties of infinite, periodic PtS2 chains. Special emphasis is put on identifying those intra- and interchain interactions that are responsible for the electronic and the structural properties, respectively. Using a single-chain code we first study isolated planar and helical PtS2 chains. Subsequently, the same method is applied in studying the chains when being surrounded by two K counterions per PtS2 unit. Finally, we study the full three-dimensional crystal structure of K2PtS2 both without and with the K atoms. The results are compared with experimental information on crystalline materials containing PtS2 chains surrounded by K, Na, or Rb counterions. Also the effects of spin–orbit couplings are examined. It is found that the neutral chains have structural properties different from the charged 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 experiment. 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 into being semiconducting. Finally, spin–orbit couplings have some effects on the structure and band structures, in particular for the planar conformation, but do hardly change the calculated structural properties.
