Electronic states and solvation of Cu and Ag aqua ions are investigated by comparing the Cu(2+) + e(-)--> Cu(+) and Ag(2+) + e(-)--> Ag(+) redox reactions using density functional-based computational methods. The coordination number of aqueous Cu(2+) is found to fluctuate between 5 and 6 and reduces to 2 for Cu(+), which forms a tightly bound linear dihydrate. Reduction of Ag(2+) changes the coordination number from 5 to 4. The energetics of the oxidation reactions is analyzed by comparing vertical ionization potentials, relaxation energies, and vertical electron affinities. The model is validated by a computation of the free energy of the full redox reaction Ag(2+) + Cu(+) --> Ag(+) + Cu(2+). Investigation of the one-electron states shows that the redox active frontier orbitals are confined to the energy gap between occupied and empty states of the pure solvent and localized on the metal ion hydration complex. The effect of solvent fluctuations on the electronic states is highlighted in a computation of the UV absorption spectrum of Cu(+) and Ag(+).

A recently introduced formulation of time dependent linear response density functional theory within the plane-wave pseudopotential framework ͓J. Hutter, J. Chem. Phys. 118, 3928 ͑2003͔͒ is applied to the study of solvent shift and intensity enhancement effects of the 1 A 2 n→* electronic transition in acetone, treating solute and solvent at the same level of theory. We propose a suitable formalism for computing transition intensities based on the modern theory of polarization, which is applicable to condensed-phase and finite systems alike. The gain in intensity brought about by thermal fluctuations is studied in molecular acetone at room temperature, and in gas-phase (CH 3) 2 CO•(H 2 O) 2 at 25 K. The latter system is characterized by the appearance of relatively intense features in the low-energy region of the spectrum, attributable to spurious solvent →solute charge-transfer excitations created by deficiencies in the DFT methodology. The n→* transition can be partially isolated from the charge-transfer bands, yielding a blueshift of 0.17 eV with respect to gas-phase acetone. This analysis is then carried over to a solution of acetone in water, where further complications are encountered in the from of a solute→solvent charge transfer excitations overlapping with the n→* band. The optically active occupied states are found to be largely localized on either solute or solvent, and using this feature we were again able to isolate the physical n→* band and compute the solvatochromic shift. The result of 0.19 eV is in good agreement with experiment, as is the general increase in the mean oscillator strength of the transition. The unphysical charge transfers are interpreted in terms of degeneracies in the spectrum of orbital energies of the aqueous acetone solution.

Keywords: Density functional calculations / Fenton reaction / Alkanes / Hydroxylation / High-valent oxidoiron(IV) systems / Push effectThe key electronic structural feature of the FeO 2+ moiety, which determines its activity as an alkane hydroxylation catalyst, is the presence of low-lying acceptor orbitals, namely the 3σ* 3d z 2-2p z antibonding orbital. Both the energetic position of this orbital and the spin state of the system (which in turn also affects the 3σ* energy) depend on the surrounding ligands. We present results of density functional theory (DFT) calculations performed on a series of gas-phase complexes of2+ by substitution of ligand water molecules with L = NH 3 , CH 3 CN, H 2 S and BF 3 . The calculations reveal that the high-spin (quintet) state is favoured by the weaker σ-donating equatorial ligands, which is consistent with the literature. The high-spin configuration is more reactive because of significant exchange stabilisation of the crucial 3σ*Ȇ orbital. Once the

Oxide potentials which transfer well between different materials have to account explicitly for many-body contributions to the interaction potentials between the ions. These include dipole and quadrupole polarization effects and the compression and deformation of an oxide ion by its immediate coordination environment. Such complex potentials necessarily involve many parameters. We examine how the results of ab initio electronic structure calculations, based upon planewave DFT methods, on general configurations of ions derived from simulations at finite temperature, may be used to parameterize an "aspherical ion method" (AIM) potential (A. J. Rowley, P. Jemmer, M. Wilson and P. A. Madden, J Chem. Phys., 1998, 108, 10209). Dipoles and quadrupoles on the individual ions are obtained via a transformation of the Kohn Sham orbitals to localized orbitals on each ion, which enables a distorted charge density for each ion to be obtained. The dipoles and quadrupoles appearing in polarization parts of the AIM potential are fit to those obtained from the ab initio ionic charge densities obtained in this way. The remaining parts of the potential, describing short-range repulsive interactions between ions with compressed and deformed charge densities, are fit to the ab initio forces and the stress tensor. By using a sufficiently large and varied set of configurations on which to carry out this optimization, an excellent transferable potential is obtained.