Spectral diffusion in a fluctuating charge model of water

Area of Science:

• Computational Chemistry
• Physical Chemistry
• Molecular Dynamics

Background:

• Understanding liquid water dynamics is crucial for many chemical and biological processes.
• Previous models, like SPC/E, provided insights but had limitations in accurately capturing water's complex behavior.
• Vibrational echo experiments offer a window into ultrafast hydrogen bond dynamics.

Purpose of the Study:

• To investigate hydrogen bond rearrangement dynamics in liquid water using an advanced computational model.
• To compare the performance of the fluctuating charge (SPC-FQ) model against the nonpolarizable SPC/E model.
• To assess the agreement of simulation results with experimental data from vibrational echo spectroscopy.

Main Methods:

• Application of the combined electronic structure/molecular dynamics approach.
• Utilizing the fluctuating charge (SPC-FQ) model for liquid water simulations.
• Analysis of the OD stretch frequency time-correlation function for HOD in H2O.

Main Results:

• The calculated time scale for hydrogen-bond rearrangement in the SPC-FQ model is approximately 1.5 ps.
• This is significantly longer than the 0.9 ps decay observed for the nonpolarizable SPC/E water model.
• The SPC-FQ model's results show improved agreement with recent vibrational echo experimental findings.

Conclusions:

• The fluctuating charge (SPC-FQ) model provides a more accurate representation of hydrogen bond dynamics in liquid water.
• The improved agreement with experiments validates the use of advanced polarizable water models for studying liquid dynamics.
• This study highlights the importance of electronic structure/molecular dynamics methods for chemical physics research.