Coupled Cluster With Singles And Doubles Research Articles

Adiabatic electron affinities of small superhalogens: LiF2, LiCl2, NaF2, and NaCl2

Geometries and frequencies for the neutral MX2 and ionic MX2− species (M=Li, Na, and X=F, Cl) are studied by several theoretical methods: density functional theory (Becke-3-Lee-Yang-Parr) [DFT(B3LYP)], second-order many-body perturbation theory [MBPT(2)], and coupled-cluster with singles and doubles (CCSD). The geometries optimized at the CCSD/6-311+G(d) level are used in CCSD(T) calculations with a large atomic natural orbital basis to compute adiabatic electron affinities (EAad), which are found for LiF2, LiCl2, NaF2, and NaCl2 to be 5.45, 4.97, 5.12, and 4.69 eV, respectively. The highest EAs among all the atoms of the periodic table occur in the halogen atoms (fluorine, 3.40 eV; chlorine, 3.62 eV); therefore all four of these triatomic radicals are properly termed superhalogens. LiF2, LiCl2, NaF2, and NaCl2 are thermodynamically stable, and their dissociation energies computed at the CCSD with the noniterative inclusion of triples [CCSD(T)] level are 20.5, 24.9, 19.3, and 25.2 kcal/mol, respectively. LiF2−, LiCl2−, NaF2−, and NaCl2− are more stable than their neutral parents with CCSD(T) dissociation energies of 69.5, 58.7, 49.0, and 52.5 kcal/mol, respectively. The computed vertical electron detachment energies of LiF2−, LiCl2−, NaF2−, and NaCl2− are 6.51, 5.88, 6.18, and 5.77 eV, respectively, which are in nice agreement with the values calculated by Scheller and Cederbaum by the Green–Function method.

Theoretical Studies of Inorganic and Organometallic Reaction Mechanisms. 11. Migratory Insertion of Coordinated Nitric Oxide into Cobalt−Carbon Bonds

The migratory insertion reaction of NO into the Co−CH3 σ-bond in the cobalt cyclopentadienyl complex CpCo(NO)(CH3) (2), both with and without the assistance of an incoming ligand (PH3, 1), has been studied using ab initio molecular orbital and density functional theory (DFT) methods. The insertion without PH3 association (Mechanism I) occurs with an activation energy of 10−20 kcal/mol, and the intermediate, CpCoN(O)CH3 (3a), forms with an endothermicity of 8−17 kcal/mol at the DFT-B3LYP and coupled cluster with singles and doubles (CCSD) levels of theory. The overall reaction to the product, CpCoN(O)CH3(PH3) (5b), was exothermic by −10 to −16 kcal/mol depending on the level of theory. An alternative mechanism II which begins with PH3 association and NO bending is endothermic by 16−18 kcal/mol and is immediately followed by a NO insertion barrier of 19−34 kcal/mol for an overall barrier of 35−52 kcal/mol. Therefore, Mechanism I is the favored pathway. This result is in very good agreement with the kinetic ...