All-electron DFT modeling of SWCNT growth on iron catalysts from carbon monoxide feedstock

Electronic and geometrical structures of Fe4Cn(CO)m (n + m < or = 6) and their singly negatively and positively charged ions are computed using density functional theory with generalized gradient approximation. Isomers with CO bonded directly to the cluster iron atoms and bonded to a carbon atom chemisorbed on the cluster surface are optimized for the Fe4C2CO, Fe4C2(CO)2, Fe4C3CO, and Fe4C4CO series. Optimizations of a large number of differently shaped Fe4C4, Fe4C5, and Fe4C6 clusters are performed to find trends in preferable arrangement of carbon atoms, in particular, to determine the relative energetics of structures with single C atoms versus those with C2 dimers or C3 trimers. The computed total energies are used to estimate the energetics of the Boudouard disproportionation reactions Fe4Cn(CO)m + 00-->Fe4Cn+1(CO)m-1 + CO2.