Hydrogen bonding blues: Vibrational spectroscopy of the TIP3P water model

Abstract

The computational spectroscopy of water has proven to be a powerful tool for probing the structure and dynamics of chemical systems and for providing atomistic insight into experimental vibrational spectroscopic results. However, such calculations have been limited for biochemical systems due to the lack of empirical vibrational frequency maps for the TIP3P water model, which is used in many popular biomolecular force fields. Here, we develop an empirical map for the TIP3P model and evaluate its efficacy for reproducing the experimental vibrational spectroscopy of water. We observe that the calculated infrared and Raman spectra are blueshifted and narrowed compared to the experimental spectra. Further analysis finds that the blueshift originates from a shifted distribution of frequencies, rather than other dynamical effects, suggesting that the TIP3P model forms a significantly different electrostatic environment than other three-point water models. This is explored further by examining the two-dimensional infrared spectra, which demonstrates that the blueshift is significant for the first two vibrational transitions. Similarly, spectral diffusion timescales, evaluated through both the center line slope and the frequency–frequency time correlation function demonstrate that TIP3P exhibits significantly faster spectral dynamics than other three-point models. Finally, sum-frequency generation spectroscopy calculations suggest that despite these challenges, the TIP3P empirical map can provide phenomenological, qualitative, insight into the behavior of water at the air–water and lipid–water interfaces. As these interfaces are models for hydrophobic and hydrophilic environments observed in biochemical systems, the presently developed empirical map will be useful for future studies of biochemical systems.