Geometric and electronic structures of AlnCum (n=5-9, m=1-3) clusters: genetic algorithm combined with ab initio models

摘要

The geometries, stabilities and electronic structures of AlnCum (n = 5-9, m = 1-3) clusters were explored by using the genetic algorithm combined with ab initio methods. The geometric structures are almost spherical when the valence electrons are around the magic number 20, otherwise the structures are oblate or prolate. The stabilities of the clusters are related to both the Cu/Al ratios and the electronic configurations. The clusters with lower Cu/Al ratios have high stabilities. The molecular orbitals are in accord with the shell structures predicted by the jellium model. The 3d orbitals of the Cu atoms are localised, although their orbital energies are between the 1P and 1D jellium orbitals. The Al6Cu2 with 20 valence electrons forms closed 1S(2)1P(6)1D(10)2S(2) shells, and shows large binding energy and removal energy, large ionisation potential and small electron affinity. For the no-magic clusters, the structure deformation leads to crystal-field-like splitting of the degenerate shells and stabilises the clusters.