Takehiro Yoshikawa

Quantum proton transfer in hydrated sulfuric acid clusters: a perspective from semiempirical path integral simulations.

We have carried out path-integral molecular dynamics simulations for hydrated sulfuric acid clusters to understand acid-dissociation and hydrogen-bonded structural rearrangement processes in these clusters from a quantum mechanical viewpoint. The simulations were performed using the PM6 semiempirical electronic structure level whose parameters were modified on the basis of the specific reaction parameters strategy so that relative energies of optimized structures, as well as water binding energies reproduce ab initio and density-functional theory calculations. We have found that the acid dissociation processes, first and second deprotonation, effectively occur in a hydrated cluster with a specific cluster size. The mechanisms of the proton-transfer processes were analyzed in detail and it was found that the distance between O in sulfuric acid and O in the proton-accepting water is playing an important role. We also found that the water coordination number of the poton-accepting water is important in the proton-transfer processes.

Theoretical Study of Excess Electron Attachment Dynamics to the Guanine–Cytosine Base Pair: Electronic Structure Calculations and Ring–Polymer Molecular Dynamics Simulations

Electron attachment dynamics to the guanine (G)-cytosine (C) base pair has been studied from a theoretical viewpoint. The BH&HLYP-level calculations show that the dipole-bound planar (G-C)(-) base pair anion can convert into the nonplanar valence-bound anion with a relatively small barrier. This nonplanar valence-bound anion can further convert into a more stable form via proton-transfer through the N-H···N hydrogen-bond from the guanine to cytosine moiety. This excess electron induced proton-transfer process has been studied using quantized ring-polymer molecular dynamics simulations (RPMD) on an interpolated potential energy surface developed on the basis of the B3LYP-level calculations. We compare the RPMD results to the results of classical MD simulations and found that proton-transfer more effectively occurs in quantum RPMD simulations. Both vibrational quantization and corner-cutting mechanism are playing important roles in this proton-transfer process. We have also analyzed the correlation between the proton-transfer motion and other vibrational motions including ring-ring deformation motions using the reactive RPMD trajectories.