Ground-state geometries and stability of impurity doped clusters: Li_nBe and Li_nMg (n=1–12)

We have investigated the ground-state geometries of Li_nBe and Li_nMg(n=1–12) clusters using ab initio molecular dynamics. These divalent impurities Be and Mg induce different geometries and follow a different growth path for n>5. Li_nMg clusters are significantly different from the host geometries while Li_nBe clusters can be approximately viewed as Be occupying an interstitial site in the host. Our results indicate that Be gets trapped inside the Li cage, while Mg remains on the surface of the cluster. Mg-induced geometries become three-dimensional earlier at n=4 as compared to the Be system. In spite of a distinct arrangement of atoms in both cases the character of the wave functions in the d manifold is remarkably similar. In both cases an eight valence electron system has been found to be the most stable, in conformity with the spherical jellium model.