Coupled-cluster interpretation of the photoelectron spectrum of Ag3 (.).

We use the scalar relativistic ionized equation-of-motion coupled-cluster (IP-EOMCC) approaches to investigate the photoelectron spectrum of Ag3 (-), examining the effects of basis set, number of correlated electrons, level of applied theory including up to 3-hole-2-particle terms, and geometry relaxation. By employing an IP-EOMCC-based extrapolation scheme, we are able to provide an accurate interpretation and complete assignment of peaks and other key features in the experimentally observed spectra, including electron binding energies as high as about 6.5 eV.

Communication: Coupled-cluster interpretation of the photoelectron spectrum of Au₃⁻.

We use the scalar relativistic ionized equation-of-motion coupled-cluster approaches, correlating valence and semi-core electrons and including up to 3-hole-2-particle terms in the ionizing operator, to investigate the photoelectron spectrum of Au₃⁻. We provide an accurate assignment of peaks and shoulders in the experimental photoelectron spectrum of Au₃⁻ for the first time.

Communication: Determining the lowest-energy isomer of Au8: 2D, or not 2D.

A parallel numerical derivative code, combined with parallel implementation of the coupled-cluster method with singles, doubles, and non-iterative triples (CCSD(T)), is used to optimize the geometries of the low-energy structures of the Au8 particle. The effects of geometry relaxation at the CCSD(T) level and the combined effects of the basis set and core-valence correlations are examined and the results are compared with the corresponding second-order Møller-Plesset perturbation theory calculations. The highest-level computations, in which the single-point CCSD(T) calculations employing the correlation-consistent basis set of the cc-pVTZ quality and the associated relativistic effective core potential (ECP), both optimized for gold, and correlating the 5d(10)6s(1) valence and 5s(2)5p(6) semi-core electrons, are combined with the geometrical information obtained with the corresponding CCSD(T)/cc-pVDZ/ECP approach, favor the planar configuration, with the next three non-planar structures separated by 4-6 kcal/mol.

Aerobic oxidation of methanol to formic acid on Au8-: benchmark analysis based on completely renormalized coupled-cluster and density functional theory calculations.

The left-eigenstate completely renormalized coupled-cluster (CC) method with singles, doubles, and noniterative triples [CR-CC(2,3)] and a few representative density functional theory (DFT) approaches have been applied to methanol oxidation to formic acid on a Au8(-) cluster, which is a model for aerobic oxidations on gold nanoparticles. It is demonstrated that CR-CC(2,3) supports the previous exothermic reaction mechanism, placing the initial rate-determining transition state, which corresponds to hydrogen transfer from the methoxy species to the molecular oxygen, at about 20 kcal/mol above the reactants, less than 40 kcal/mol above the O2 and CH3O(-) species coadsorbed on Au8(-), and considerably above the remaining two transition states along the reaction pathway. The DFT calculations using the previously exploited M06 hybrid functional show reasonable agreement with CR-CC(2,3), but B3LYP offers additional improvements in the description of the relevant activation energies.

Communication: existence of the doubly excited state that mediates the photoionization of azulene.

We use the high-level electronic structure computations based on the equation-of-motion coupled-cluster (EOMCC) theory to show that the previously postulated [V. Blanchet et al., J.

The Cobalt-Methyl Bond Dissociation in Methylcobalamin: New Benchmark Analysis Based on Density Functional Theory and Completely Renormalized Coupled-Cluster Calculations.

The Co-CMe bond dissociation in methylcobalamin (MeCbl), modeled by the Im-[Co(III)corrin]-Me(+) system consisting of 58 atoms, is examined using the coupled-cluster (CC), density-functional theory (DFT), complete-active-space self-consistent-field (CASSCF), and CASSCF-based second-order perturbation theory (CASPT2) approaches. The multilevel variant of the local cluster-in-molecule framework, employing the completely renormalized (CR) CC method with singles, doubles, and noniterative triples, termed CR-CC(2,3), to describe higher-order electron correlation effects in the region where the Co-CMe bond breaking takes place, and the canonical CC approach with singles and doubles (CCSD) to capture the remaining correlation effects, abbreviated as CR-CC(2,3)/CCSD, is used to obtain the benchmark potential energy curve characterizing the Co-CMe dissociation in the MeCbl cofactor. The Co-CMe bond dissociation energy (BDE) resulting from the CR-CC(2,3)/CCSD calculations for the Im-[Co(III)corrin]-Me(+) system using the 6-31G* basis set, corrected for the zero-point energies (ZPEs) and the effect of replacing the 6-31G* basis by 6-311++G**, is about 38 kcal/mol, in excellent agreement with the experimental values characterizing MeCbl of 37 ± 3 and 36 ± 4 kcal/mol.