The classical and quantum dynamics of an excess proton in water is studied by molecular dynamics simulations. The electronic structure of the system is described by an extended multistate valence-bond Hamiltonian that allows for the breaking and formation of O-H + bonds. The proton quantum character is treated by means of an effective (path-integral) proton-transfer surface. Whereas classical simulations predict that the hydrated proton appears in a mixture of H 5 O 2 + and H 9 O 4 + structures, inclusion of proton quantization leads to the prevalence of H 5 O 2 +. The proton-transfer mechanism can be described mostly as the translocation of a transient H 5 O 2 + structure across the water hydrogen-bond network. The computed lifetime of a particular H 5 O 2 + is close to 2 ps, a value compatible with experimental estimates.

We introduce a new theoretical formalism to compute solid-state vibrational circular dichroism (VCD) spectra from molecular dynamics simulations. Having solved the origin-dependence problem of the periodic magnetic gauge, we present IR and VCD spectra of (1S,2S )-trans-1,2-cyclohexanediol obtained from first-principles molecular dynamics calculations and nuclear velocity perturbation theory, along with the experimental results. As the structure model imposes periodic boundary conditions, the common origin of the rotational strength has hitherto been ill-defined and was approximated by means of averaging multiple origins. The new formalism relies on the velocity representation of VCD and the time-correlation function, whose symmetry properties are exploited to reconnect the periodic model with the finite physical system. It restores the gauge freedom of finite models, but still allows fully accounting for non-local spatial coupling terms from the gauge transport term. We show that even for small simulation cells the rich nature of solid-state VCD spectra found in experiments can be reproduced to a very satisfactory level. While the general workflow to compute solid-state VCD spectra relies on the interplay of experimental data and theoretical simulation, expressions of VCD in liquid state and for isolated systems can be derived as simplification of the general equations.

Electronic Structure and Solvation of Copper and Silver Ions: A Theoretical Picture of a Model Aqueous Redox Reaction -[DFT calculations]. -(BLUMBERGER, J.; BERNASCONI, L.; TAVERNELLI, I.; VUILLEUMIER, R.; SPRIK*, M.; J. Am. Chem. Soc. 126 (2004) 12, 3928-3938; Dep. Chem., Univ. Cambridge, Cambridge CB2 1EW, UK; Eng.) -Schramke 23-002