Gap opening in the most stable phases of K₃ Terphenyl compound

The crystalline structure of potassium intercalated para-terphenyl has been theoretically investigated using a van der Waals Density Functional (vdW–DF) scheme. The incorporation of K atoms into the pristine terphenyl crystal continuously improves the compound stability up to a 3:1 stoichiometry. In addition to confirming previously studied structures, several new crystalline phases showing inedited patterns -small clusters formed by four to six potassium atoms- have been found, in particular, for the more stable K₃Terphenyl crystals. Initially, the band structure of these compounds shows metallic features. Nevertheless, a better description of the electronic structure using hybrid functionals that go beyond generalized-gradient-approximation (GGA) reveals that potassium electrons completely filled three sub–bands that develop at the conduction band bottom. Consequently, these stable phases should be discarded as metallic phases able to show superconductivity at low temperatures. Moreover, our study evidences that due to the important electronic correlations shown by these compounds only computational schemes that go beyond GGA are able to provide robust conclusions. (paper)