The planar-to-tubular structural transition in boron clusters from optical absorption

The optical response of the lowest-energy isomers of the B-20 family is calculated using time-dependent density-functional theory within a real-space, real-time scheme. Significant differences are found among the absorption spectra of the clusters studied. We show that these differences can be easily related to changes in the overall geometry. Optical spectroscopy is thus an efficient tool to characterize the planar-to-tubular structural transition, known to be present in these boron-based systems.