Clustering of atoms and the metal-non-metal transition

Several liquid alloys of alkali metals (A=Li, Na, K, Rb, Cs) with group-IV (B=Si, Ge, Sn, Pb) alloys show strongly anomalous electrical transport properties for compositions AB and/or A4B. In some cases a nearly complete charge transfer leads to a nearly non-metallic behaviour (for example in Li4Sn and KPb). These anomalies are explained in terms of calculations of the electronic structure, using a tight-binding model and taking into account on-site and nearest-neighbour Coulomb interactions, clustering of B atoms and short-range order. In particular near the composition AB the presence of tetrahedral clusters B4 4- has a large influence on the properties on the liquid alloy