A theoretical study of structural and electronic properties of alkaline-earth fluoride clusters

The structural evolution and variation of electronic properties of alkaline-earth metal fluoride clusters (MF2)n (M = Mg, Ca, Sr, Ba; n = 1–6) are investigated using density functional theory. All these clusters demonstrate ionic-bonding dominated through all sizes considered here, and generally show a preference of 3D structures when n ⩾ 4. It is found that the structural evolution of (MgF2)n clusters are distinct from the rest of the alkaline-earth clusters owing to the competitive interplay of much smaller ionic radius of Mg and the stronger Mg–F bond. In the ground state configurations, (MgF2)n clusters prefer the planar building units, whereas the rest of the (MF2)n clusters prefer the 3D building units of a M2F3 type maximizing the coordination number of the constituent metal atoms. The variations of the binding energy, the ionization potential, the electron affinity and the HOMO–LUMO gap with the cluster size are explained in terms of the change in the ionic radius and the basicity of the constituent metal ions in going from (MgF2)n to (CaF2)n, (SrF2)n, and (BaF2)n.