Old puzzle of incommensurate crystal structure of calaverite AuTe2 and predicted stability of novel AuTe compound

Abstract

Gold is a very inert element, which forms relatively few compounds. Among them is a unique material-mineral calaverite, AuTe2. Besides being the only compound in nature from which one can extract gold on an industrial scale, it is a rare example of a natural mineral with incommensurate crystal structure. Moreover, it is one of few systems based on Au, which become superconducting (at elevated pressure or doped by Pd and Pt). Using ab initio calculations we theoretically explain these unusual phenomena in the picture of negative charge-transfer energy and self-doping, with holes being largely in the Te 5p bands. This scenario naturally explains incommensurate crystal structure of AuTe2, and it also suggests a possible mechanism of superconductivity. An ab initio evolutionary search for stable compounds in the Au-Te system confirms stability of AuTe2 and AuTe3 and leads to a prediction of an as yet unknown stable compound AuTe, which until now has not been synthesized.