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

摘要

The structural evolution and variation of electronic properties of alkaline-earth metal fluoride clusters (MF_2)_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 (MgF_2)_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, (MgF_2)_n clusters prefer the planar building units, whereas the rest of the (MF_2)_n clusters prefer the 3D building units of a M_2F_3 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 (MgF_2)_n to (CaF_2)_n, (SrF_2)_n, and (BaF_2)_n.