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

Nakazawa, Tetsuya

Geometries and energy separations of various low-lying electronic states of iron trimer (Fe) are investigated by CCSD and CCSD(T) calculations. The ground state is found to be a A' state with C symmetry, whereas a nearly isoenergetic state, A (C), is degenerate to the ground state. The ground and five low-lying states with a spin multiplicity of 13 are found below 0.20 eV at the CCSD(T) level. On the other hand, the low-lying states with spin multiplicities of 9, 11, and 15 appear only above 0.20 eV. From detailed natural bond orbital (NBO) analyses, Fe has Fe-Fe bonds comprised of -bond orbitals only in -spin part with higher s-character in low-lying states with a spin multiplicity of 13. The polarization coefficients indicate that the bonds are nearly complete covalent bonds with little polarization.