A theoretical investigation on geometry and electronic structure of small FemSn nanoclusters (1 ⩽ m, n ⩽ 4)

The equlibrium structure and relative stability of FemSn clusters (1 ⩽ m, n ⩽ 4) were investigated using density functional theory and second order Møller–Plesset perturbation theory. In general, the S doping leads to significant changes in the geometry of the studied clusters. It is evident that the FeFe distances are elongated upon the sequential addition of sulfur. Relative stabilities of these clusters were analyzed based on the variation of their averaged binding energies, and FeS bond formation energies. Based on quantum theory of atoms in molecules (QTAIMs), the non-covalent character of the FeS bond is increased in the FemSn clusters as the corresponding bond critical points (BCPs) showed more positive ∇2ρBCP value than those of the FeS molecule. On the other hand, the estimated electron charge density values at FeFe BCPs lie in the order of 0.11–0.22 au. The corresponding Laplacian values in all clusters are negative and are the result of the interaction between two open-shell systems.