Geometries and electronic states of iron trimer (Fe₃) by CCSD and CCSD(T) calculations

Geometries and energy separations of various low-lying electronic states an iron trimer (Fe3) are investigated by coupled-cluster singles doubles (CCSD) plus perturbative triples [CCSD(T)] calculations. The ground state is found to be a 13A? with Cs symmetry, whereas nearly isoenergetic state, 13A1 (C2v), degenerate the state. five spin multiplicity 13 below 0.20 eV at CCSD(T) level. On other hand, multiplicities 9, 11, 15 appear only above eV. From detailed natural bond orbital analyses, Fe3 has Fe–Fe bonds composed ?-bond orbitals in the?-spin part higher s-character 13. polarization coefficients indicate that ?Fe–Fe complete covalent little polarization.