Figure 2.

(a) Idealized ccp M₄₀ core of 1^6– (green for surface atoms and purple for the fully interstitial M₄ tetrahedron) and (b) its real M₄₁ metal core obtained by adding a further Ni atom (orange) to the top triangular face [yellow for three disordered Ni/Pd sites at the center of the (111) faces].