Ab initio calculations for mixed clusters of lead and alkali elements, and implications for the structure of their solid and liquid alloys

Ab initio density functional calculations for mixed clusters of Pb and alkali elements demonstrate the high stability of the octet clusters A4Pb in the case of light alkali metals, that is for A=Li or Na. This justifies the observed anomalies at the composition of 20% Pb in the liquid alloys of Pb with Li and Na. The calculations also show the high stability of the Zintl clusters A4Pb4, which explains the crystalline structure of the equiatomic solid compounds of Pb with Na, K, Rb and Cs, and the persistence of the Zintl complexes in the melt. The absence of Zintl clustering in the Li alloys is due to an atomic size effect.