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Impressum
(c) 2002 BMO

"The Infrared Spectrum of p-Benzoquinone in Water Obtained from a Hybrid Molecular Dynamics Simulation"
Marco Nonella, Gerald Mathias, Paul Tavan
J. Phys. Chem. A 107, 8638 - 8647 (2003)


Abstract:
The accurate description of vibrational spectra of isolated dye molecules like quinones has become a standard task in computational chemistry due to the progress of density functional theory. This is by no means the case for solution spectra. To contribute to this issue, we have carried out a QM/MM hybrid molecular dynamics (MD) simulation of p-benzoquinone in water as to derive its IR spectra. We have explored two different computational procedures, which allow to calculate an IR spectrum from such a dynamics simulation. One is based on Fourier transforms of autocorrelation functions and the other on instantaneous normal mode analyses of snapshots. We show that both approaches are valid and yield similar vibrational frequencies. For a detailed comparison of computed band widths and intensities, however, our 17.5 ps QM/MM-MD trajectory turned out to be too short. The analysis of the trajectory also demonstrates that on the average three water molecules form distinct solvation shells around each of the quinone C=O groups. These hydrogen bonded water molecules exchange on a time scale of about 2.5 ps. Computations on small, rigid quinone-water clusters compare reasonably well with the dynamics approach concerning the spectral positions of the quinone IR bands. Of course, the inhomogeneous broadening of IR bands, which is covered by the dynamics calculations, is inaccessible to the static cluster approach.

BMO authors (in alphabetic order):
Gerald Mathias
Marco Nonella
Paul Tavan

Assoziierte Projekte:
Vibrational Spectra of Quinones
QM/MM hybrid descriptions of solutes in complex solvents


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