Dynamical Accuracy of Water Models on Supercooling

Area of Science:

• Physical Chemistry
• Computational Physics
• Materials Science

Background:

• Supercooled water exhibits complex dynamics within the experimentally challenging "no man's land" (NML) region.
• Molecular dynamics (MD) simulations offer insights into water's structural and dynamical properties at low temperatures.
• Previous MD studies have explored water behavior in NML, but discrepancies with experimental data persist.

Purpose of the Study:

• To compare the accuracy of different molecular dynamics (MD) water models in reproducing experimental quasielastic neutron scattering (QENS) data.
• To assess the temperature dependence of MD simulation accuracy for supercooled water dynamics in the NML.
• To identify discrepancies between simulated and experimental water dynamics at the molecular level.

Main Methods:

• Utilized molecular dynamics (MD) simulations with one-, three-, and four-body water models.
• Compared simulation results with experimentally measured quasielastic neutron scattering (QENS) spectra.
• Analyzed the agreement between simulated and experimental data across a range of temperatures, focusing on the NML.

Main Results:

• Agreement between MD simulations and experimental QENS data significantly degrades as temperature decreases toward the deeply supercooled regime.
• The local dynamics of water molecules are poorly reproduced by the MD models, more so than macroscopic properties like the diffusion coefficient.
• Discrepancies highlight limitations in the molecular mechanisms captured by current MD water models.

Conclusions:

• Current MD models exhibit significant limitations in accurately describing the local dynamics of supercooled water in the NML.
• Simulated structural and dynamical properties of water in NML should be interpreted with caution due to poor agreement with experimental data.
• Further development of MD water models is needed to improve the representation of molecular mechanisms governing water dynamics.