  It is shown that the long-standing puzzle of incommensurate crystal structure
of AuTe$_2$ can be solved, if this material is considered as a negative
charge-transfer system. Using modern computational methods, we demonstrate that
charge redistribution associated with incommensurate modulations of crystal
structure occurs not so much on Au, but predominantly on Te sites. This
substantially reduces Coulomb energy costs for creating such a unique crystal
structure. The same mechanism also explains superconductivity of doped
AuTe$_2$. Exploring different Au-Te compositions, we also discovered a
previously unknown compound AuTe, which theoretically is very stable, and we
predict its crystal structure.
