Interaction of Cobalt Atoms, Dimers, and Co4 Clusters with Circumcoronene: A Theoretical Study

Abstract

We study the interaction of circumcoronene molecule C54H18 with cobalt in the form of atoms, dimers, and clusters of four atoms. We find that the cobalt atom prefers to be on a hollow site in the edge zone. The cobalt dimer is bonded perpendicularly to another different hollow site in the edge zone. The Co4 cluster adopts a tetrahedral shape with a face parallel to circumcoronene, placing each of the three atoms over contiguous hollow sites, starting from the edge. Cobalt remains bonded to circumcoronene as Co2 molecules or Co4 clusters, rather than spread as isolated atoms, because the cobalt–cobalt interaction is stronger than the cobalt–carbon bond. The interaction with cobalt clusters induces a small magnetic moment on circumcoronene. The magnetic moment of cobalt is reduced when bonding to circumcoronene. There is charge transfer between those systems and its direction depends on the relative position of the cluster with respect to circumcoronene. We then propose that the presence of cobalt over circumcoronene or similar polycyclic-aromatic hydrocarbons can be detected in experiments, looking at the carbon isomer shift which arises due to the contact charge densities at the nuclei.