Abstract
In this work, we address one of the most fundamental questions in cluster science─how do the structure and properties evolve from clusters to crystals? Using density functional theory (DFT), we focus our study on the evolution of structure and magnetism in iron-chloride systems, from clusters to monolayers. The choice of this system is motivated by the recent experimental confirmation of one of the author's earlier theoretical prediction that the FeCl(2) cluster is magnetic with a spin magnetic moment of 4 μ(B) localized at the Fe site, while its dimer, Fe(2)Cl(4), is antiferromagnetic. Similarly, FeCl(3) cluster is magnetic with a total spin magnetic moment of 5 μ(B), with 4 μ(B) localized at the Fe site and 1 μ(B) distributed over the Cl sites. The dimer clusters Fe(2)Cl(4) and Fe(2)Cl(6) have an antiferromagnetic ground state, and upon Li-functionalization, both can be magnetically transformed from antiferromagnetic to ferromagnetic states. In contrast, FeCl(2) and FeCl(3) monolayers exhibit different magnetic ground states in their periodic forms: FeCl(2) is ferromagnetic (FM), but in FeCl(3), the antiferromagnetic (AFM) and FM states are energetically nearly degenerate. Such a difference arises due to the different chemical coordination of the Fe atoms with the Cl atoms, caused by their different oxidation states, which is +2 in FeCl(2) and +3 in FeCl(3), respectively. Interestingly, Li-functionalization allows both FeCl(3) and FeCl(2) monolayers to be ferromagnetic. Our study highlights that several, but not all, electronic and magnetic characteristics of isolated clusters are preserved in the extended periodic structures. This systematic investigation of iron-halide clusters is expected to inspire further experimental and theoretical exploration into the magnetism of other transition metal halides.