(BAl12)Cs: A cluster-assembled solid

First-principles calculations on the geometry and stability of AlnBm clusters have been carried out to examine the effect of size, composition, and electronic-shell filling on their relative stability, It is shown that although Al and B are both trivalent, a BAl12 cluster is more stable than an Al-13 by 3.4 eV. The enhanced stability is shown to arise due to the relaxation of surface strain in the Al cage when the central Al is replaced by a smaller B atom. Replacement of an additional Al by B to produce B,all, results in deformation of the icosahedral BAl12 cage and reduces the stability. The possibility of forming crystals using BAl12 and CS is examined via total-energy calculations. It is shown that a solid with icosahedral or cuboctahedral BAl12 and Cs and having the CsCl structure is metastable and could be synthesized.