Ground-state geometries and stability of impurity doped clusters:LinBeandLin

Abstract

We have investigated the ground-state geometries of Li n Be and Li n Mg (nϭ1-12) clusters using ab initio molecular dynamics. These divalent impurities Be and Mg induce different geometries and follow a different growth path for nϾ5. Li n Mg clusters are significantly different from the host geometries while Li n Be 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 nϭ4 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.

Electronic structure and thermochemical properties of silicon‐doped lithium clusters LinSi0/+, n = 1–8: New insights on their stability

“…The global minimum of Li 8 Si is a C 2 structure 8n.1 in which two Li atoms are capped on two opposite triangular faces of Li 6 Si (O h ). Similar to the case of Li 7 Si, the coordination number of silicon is only equal to 6 in 8n.1. Two structures 8n.2 (C 2v , 1 A 1 ) and 8n.3 (C s , 1 A 0 ) that are formed by adding one excess Li into Li 7 Si (7n.2) are the next low-lying isomers with a coordination number of 7, whereas the high symmetry 8n.4 (C 4v , 1 A 1 ) in which Si is located at the center of the antiprism square cage Li 8 is much less stable with relative energy of 17.8 kcal/mol.…”

“…It is interesting to note that the structure 7n.1 (C s , 2 A 0 ) in which one Li atom is capped on one of the triangular faces of Li 6 Si (6n.1) is the lowest lying isomer for Li 7 Si. Its C 3v counterpart 7n.4 (C 3v , 2 A 1 ) turns out to be a transition state with one imaginary frequency.…”

“…Three different isomers, namely from 7n.1 to 7n.3, are located for Li 7 Si. It is interesting to note that the structure 7n.1 (C s , 2 A 0 ) in which one Li atom is capped on one of the triangular faces of Li 6 Si (6n.1) is the lowest lying isomer for Li 7 Si.…”

“…[14] However, the model cannot be applied when the number of valence electrons of enhanced stability species is not the same for different systems. For the impure lithium clusters doped by group IIA and IIIA elements (Be, Mg, B, and Al), [7][8][9][10] the most stable species are found to possess eight valence electrons, occupying orbitals of 1S 2 and 2P 6 in the PSM. This magic number of eight valence electrons is observed in cases of Li n Ge [13] and Li n Sn, [12] but it is failed for carbon-doped lithium clusters…”

“…[5,6] According to this modified model, the dopant induces a perturbation and the ordering of the single particle energy levels is changed either to (1S 2 1P 6 2S 2 1D 10 2P 6 ) if the impurity is more electronegative than the host atoms, or to (1S 2 1P 6 1D 10 2S 2 1F 14 2P 6 ) if the central dopant is less electronegative. Through the PSM model, the electronic structure and stability motifs of many metal clusters were consistently rationalized, including the doped lithium clusters Li n M with impurities M as beryllium (Be), magnesium (Mg), [7] boron (B), [8,9] aluminum (Al), [10] carbon (C), [11] tin (Sn), [12] germanium (Ge), [13] and oxygen (O). [14] However, the model cannot be applied when the number of valence electrons of enhanced stability species is not the same for different systems.…”