No abstract

The DFT-D method is shown to yield interaction energies between biologically important groups to an accuracy comparable to that obtained using state-of-the-art ab initio methods.

Density function theory calculations reveal that the GrubbsHoveyda olefin metathesis pre-catalyst is activated by the formation of a complex in which the incoming alkene substrate and outgoing alkoxy ligand are both clearly associated with the ruthenium centre. The computed energies for reaction are in good agreement with the experimental values, reported here.

Quantum mechanical bond orders are obtained from integration of the exchange–correlation density between topological atoms.

High-level electronic structure calculations have been carried out to identify stationary structures on the potential energy surface of a number of acids in water clusters, with 4 or 7 solvent molecules. The calculations employed a 6-311++g** basis with correlation at the MP2 and DFT (B3LYP) levels. Both DFT and a smaller basis set tended to favor the zwitterionic, compared to the unionized, structures. The cooperative nature of the ionization process was especially evident, with single and double layers of three water molecules separating the ionized groups and actively participating in ionization. For the pure water clusters, both (H2O)5 and (H2O)8 had similar relative energies for unionized, zwitterionic, and transition-state structures, showing that a range of structures and ionization mechanisms can occur in bulk water. For HF and H2S, the relative energetics and stationary structures showed ionization to be more favorable in the larger clusters. The trend of earlier transition states for the stronger acids was identified for HF, H2S, and H2SO3.