Abstract
In the present work, we introduce two new metrics i.e. hydrogen-bond strength and charge-transfer between the donor/acceptor water molecules as a measure of hydrogen-bond rearrangement dynamics. Further, we also employ a simple model based on energy flux through the donor-acceptor water pairs to quantify the extent of the local hydrogen-bond network reorganization. Most importantly, we report a linear relationship between the OH stretch frequency and the charge and energy transfer through donor-acceptor water pairs. We demonstrate that the vibrational frequency fluctuations, which are used to determine third-order non-linear spectroscopic observables like the short-time slope of three pulse photon echo, can be used as an analog of the fluctuations in the hydrogen-bond strength and charge-transfer. The timescales obtained from our hydrogen-bond strength correlation and charge-transfer correlation decay are in excellent agreement with the computed frequency-time correlation function, as well as with recent vibrational echo experiments.
Highlights
In present work we have introduced the HB strength and HB charge-transfer between the donor/ acceptor water molecules as a new metric of predicting the HB rearrangement dynamics
The great appeal of these metrics lies in the fact that they do not rely on any HB definition and can be readily obtained from ab-initio molecular dynamics (MD) simulations
We have demonstrated the ablity of the introduced metrics to represent spectral observables of non-linear spectroscopic experiments like 3PEPS
Summary
The ab-initio MD simulation of liquid water was performed using the second-generation Car-Parrinello MD method[46,47,48], as implemented in the mixed Gaussian and plane waves code CP2K/Quickstep[49,50]. Therein, the Kohn-Sham orbitals are expanded in contracted Gaussians, whereas the electronic charge density is represented using plane waves. For the former, we use an accurate molecularly optimized double-ζ basis set with one additional set of polarization functions (DZVP)[51], while for the latter a density cutoff of 280 Ry was employed. The system was initially equilibrated in the canonical NVT ensemble for 10 ps followed by a production run in the microcanonical NVE ensemble for additional 25 ps
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