The very unusual structural features observed in the recently characterized high pressure novel K-Ag alloys can be rationalized using simple electron counting rules and a moment analysis of the electronic density of states. The stability of the alloys is attributed to almost complete electron transfer from K $4s$ bands to Ag $5s$ bands and spatially extended Ag $5p$ bands. This allows for efficient Ag-Ag bonding interactions at an unusually long distance of 5.54 Å and exceptionally short K-K bonds due to reduced repulsive interactions between the ${\mathrm{K}}^{+}$ ions. The general principles developed here are applicable to the understanding of the structure and bonding of other high pressure intermetallic alloys.

• Received 8 January 1999

DOI:https://doi.org/10.1103/PhysRevLett.82.4472