The C-C pair in the vicinity of a bcc Fe bulk vacancy: electronic structure and bonding

C-Fe and C-C interactions near a bee Fe vacancy were analysed using DFT calculations. A cell containing 14 atoms was used to simulate the local environment of the Fe vacancy. Carbon atoms were positioned in their local energy minimum configurations. The most stable positions for the C atoms in the vacancy region were found at about 1.23 angstrom from the vacancy centre and near the first nearest-neighbour octahedral sites. Changes in the electronic structure of Fe atoms near a vacancy were analysed. Fe-Fe bonds surrounding the vacancy weaken their bond when the C atoms are present. This bond weakening is a consequence of C-Fe bond formation. The Fe-C interactions occur mainly via Fe 4s orbitals with a lesser participation of Fe 3p orbitals. There is an electron transfer to the C atoms from their Fe nearest neighhours. The C-C interaction was also analysed. For the C-C distance of 1.462 angstrom, there is a bonding between the C atoms. The C-C interaction is stronger than the C-Fe interactions. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.