Ground-state geometries and stability of Na_nMg (n=1-2) clusters using ab initio molecular dynamics method

Abstract

The ground-state geometries, energetics and the stability of Na_nMg (n=1-12) clusters are studied using ab initio molecular dynamics method. Our results indicate that the ground-state geometries of large clusters ( n ≥ 6) are different from those of Na_nAL clusters where a trivalent impurity Al is added to the same monovalent host Na. Other features observed are an early appearance of 3-dimensional structure and a pentagonal growth path from n=6 up to n=11. As expected, the ground-state geometry of Na₁₂Mg is not an icosahedron but can be viewed as a distorted form of one of the low lying geometries of Na₁₃ cluster. In the energetically favored structures impurity atom Mg is never located at the center of the cluster. The stability analysis based on the energetics shows Na₆Mg (8 valence electrons) to be the most stable. In addition there is a remarkable even-odd pattern observed in the dissociation energy and the second difference in energy which is absent in earlier studies of Na_nAL and Li_nAl clusters.