"Understanding the Origins of Dipolar Couplings and Correlated Motion in the Vibrational Spectrum of Water"Matthias Heyden, Jian Sun, Harald Forbert, Gerald Mathias, Martina Havenith, and Dominik Marx
J. Phys. Chem. Lett., 2012, 2135-2140
The combination of vibrational spectroscopy and molecular dynamics simulations provides a powerful tool to obtain insights into the molecular details of water structure and dynamics in the bulk and in aqueous solutions. Applying newly developed approaches to analyze correlations of charge currents, molecular dipole fluctuations and vibrational motion in real– and k–space, we compare results from non–polarizable water models, widely used in biomolecular modeling, to ab initio molecular dynamics. For the first time we unfold the infrared response of bulk water into contributions from correlated fluctuations in the three–dimensional, anisotropic environment of an average water molecule, from the OH–stretching region down to the THz regime. Our findings show that the absence of electronic polarizability in the force field model results not only in differences in dipolar couplings and infrared absorption, but also induces artifacts into the correlated vibrational motion between hydrogen–bonded water molecules, specifically at the intramolecular bending frequency. Consequently, vibrational motion is partially ill–described with implications for the accuracy of non–self–consistent, a posteriori methods, to add polarizability.
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