First-principles studies on orientational ordering of atomic clusters in Cd₆Ca

First-principles structural optimizations are carried out for 1/1 cubic approximant Cd6Ca. Newly proposed structure by Gómez and Lidin is used as the starting structure for the structural optimizations. The optimized structure is more stable than the non-optimized one by several eV. Two structures, which are almost degenerate before the structural optimizations, are split by about 100 meV per unit cell after the structural optimizations. Clusters are deformed to relax interatomic distances and most of the neighbouring Cd–Cd distances close to that of hcp-Cd. Relaxed structures of clusters depend on the structure of the innermost shells of adjacent clusters.