Structure and Properties of Fe4 with Different Coverage by C and CO

Abstract

The electronic and geometrical structure of neutral and singly charged Fe4C2, Fe4C(CO), Fe4(CO)2, Fe4C2CO, Fe4C(CO)2, Fe4C3, and Fe4(CO)3 are studied using density functional theory with a generalized gradient approximation. It is found that the Fe4C2 and Fe4C2(CO) species possess two isomers with separated and dimerized carbon atoms. The latter isomers are lower in total energy by ∼0.3 eV. The Fe4C3 species possess three isomers corresponding to: a C2 dimer and one separated carbon atom (the lowest energies), a C3 trimer (intermediate energies), and three separated carbon atoms (the highest energies). The lowest energy dissociation channel corresponds to the loss of CO, except for Fe4(CO)2 and Fe4C(CO)2+, where the loss of carbon dioxide is the lowest. The computed total energies are used to estimate the energetics of the Boudouard-like disproportionation reactions, Fe4Cn(CO)m + CO → Fe4Cn+1(CO)m-1 + CO2. It is found that the most exothermic reaction in the series is Fe4C(CO)+ + CO → Fe4C2+ + CO2 (by ∼0.3 eV).