Theoretical study on spin polarization in small aluminum clusters

Geometric optimizations of neutral Al-n (n = 2-11) clusters at B3LYP/6-31+G(d) level of theory demonstrate that small aluminum clusters are spin-polarized in ground state. Specifically, Al-n ( n = 3, 5, 7, 9, and 11) clusters are spin doublets, Al-n ( n = 2, 4, 6, and 8) are triplets, whereas Al-10 is a singlet. The spin polarizability decreases as the size of the cluster increases. The electronic spin polarization is mainly attributed to the atomic 3p electrons of aluminum atoms each of which has a nonzero orbital and spin angular momenta, respectively. Among all the clusters, Al-2 is the most spin-polarized; its evident triplet stability and electronic structural properties are partially ascribed to its nuclear spins, based on the calculations of indirect nuclear spin-spin coupling constants at B3LYP/6-311+G(3df) level of theory. As the size of the cluster increases, the influence of nuclear spins on electronic spin polarization declines due to the multiple couplings.