First-principles calculations were performed to study the structure and stability of the Al-46 cluster. The results suggest two competing structural motifs, the spherical endohedral cage and layer-stacking structures. It is shown that although medium-sized Al clusters tend to form layered structures (i.e., fcc fragments with a stacking fault), a spherical endohedral cage configuration is also an important structural motif for the magic Al-46 cluster. Besides, the cluster ions were also studied, and the calculated PES of the Al-46(-) isomer with the minimum of free energy is in better agreement with the experimental PES data. (c) 2012 Elsevier B.V. All rights reserved.