title: The Energy Difference between the Triply-Bridged and All-Terminal Structures of Co₄(CO)₁₂, Rh₄(CO)₁₂, and Ir₄(CO)₁₂: A Difficult Test for Conventional Density Functional Methods.
abstract: The M4(CO)12 molecules Co4(CO)12, Rh4(CO)12, and Ir4(CO)12 have two low-lying structures, the all-terminal structure with Td symmetry and the triply bridged structure with C3v symmetry. A total of 45 density functional theory (DFT) methods have been used to predict structures and vibrational frequencies for Co4(CO)12, Rh4(CO)12, and Ir4(CO)12. The different DFT methods show a broad range of energy differences ΔE = E(Td) - E(C3v). For Rh4(CO)12, none of the 45 DFT predictions is within 11 kcal/mol of the 2005 experimental value of 5.1 ± 0.6 kcal/mol reported by Allian and Garland (Dalton Trans. 2005, 1957 - 1965). For the challenging Ir4(CO)12 molecule, 21 DFT methods predict the correct Td structure, while 24 DFT methods predict the C3v structure to lie lower in energy. This research reveals many peculiar problems in the computation of the vibrational frequencies for the all-terminal structure.
authors.affiliation: Key Laboratory for Advanced Materials and Department of Chemistry, East China University of Science and Technology , Shanghai 200237, China.
authors.forename: Hairong
authors.initials: H
authors.lastname: Ding
authors.affiliation: Key Laboratory for Advanced Materials and Department of Chemistry, East China University of Science and Technology , Shanghai 200237, China.|Center for Computational Quantum Chemistry, University of Georgia , Athens, Georgia 30602, United States.
authors.forename: Yunxiang
authors.initials: Y
authors.lastname: Lu
authors.affiliation: Center for Computational Quantum Chemistry, University of Georgia , Athens, Georgia 30602, United States.
authors.forename: Yaoming
authors.initials: Y
authors.lastname: Xie
authors.affiliation: Key Laboratory for Advanced Materials and Department of Chemistry, East China University of Science and Technology , Shanghai 200237, China.
authors.forename: Honglai
authors.initials: H
authors.lastname: Liu
authors.affiliation: Center for Computational Quantum Chemistry, University of Georgia , Athens, Georgia 30602, United States.
authors.forename: Henry F
authors.initials: HF
authors.lastname: Schaefer