Theoretical Study of the Spin Competition in Small-Sized Al Clusters

Stern-Gerlach (SG) experiments on aluminum clusters indicate that some small-sized aggregates exhibit a deflection signal consistent with the existence of magnetic moments. However, in the particular case of Al6 and Al8 clusters, electronic structure investigations show ambiguity on the 0 K ground spin state. In this work extensive computations of the electronic structure have been carried out in order to determine the ground state of these structures. Electron correlation has been introduced at MP2, MP4, and CCSD(T) theory level as well as by DFT computations with different density functionals. DFT-based Born-Oppenheimer molecular dynamics results at different simulation temperatures complete this investigation. One of our main conclusions is that singlet spin states are systematically the more stable configuration at 0 K. These Al clusters exhibit almost degenerate electronic structures at singlet and triplet spin states. The geometries are similar, and the paths connecting both structures allow an intersystem crossing through a spin-orbit coupling mechanism, indicating a dynamical interchange of both spin states at finite temperatures.