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The Boson peak in supercooled water
Pradeep Kumar1, K Thor Wikfeldt, Daniel Schlesinger
1Center for Studies in Physics and Biology, The Rockefeller University, New York, NY 10021, USA. pradeep.kumar@rockefeller.edu
Scientific Reports
|June 18, 2013
Summary
The Boson peak in supercooled water originates from low-density liquid behavior, not just confinement. These vibrational modes are extended and linked to transverse phonons in ice Ih.
Area of Science:
- Physical Chemistry
- Condensed Matter Physics
- Biophysics
Background:
- The Boson peak is an experimentally observed phenomenon in supercooled liquids, including water.
- Its origin in water, especially in confined systems and hydration layers, remains debated.
- Understanding the Boson peak is crucial for characterizing the dynamics of supercooled water.
Purpose of the Study:
- To investigate the origin of the Boson peak in supercooled water using molecular dynamics simulations.
- To determine if confinement is essential for the Boson peak's emergence.
- To explore the relationship between the Boson peak and the liquid's structural and dynamic properties.
Main Methods:
- Extensive molecular dynamics simulations using the TIP4P/2005 water model.
- Analysis of vibrational modes and their spatial characteristics.
- Comparison of simulation results with experimental data for bulk, nanoconfined, and hydration water.
Main Results:
- The Boson peak onset in bulk water correlates with a transition to a low-density-like liquid state below the Widom line.
- Simulated Boson peak frequencies and onset temperatures match experimental data for nanoconfined water.
- The Boson peak is not solely an artifact of confinement, suggesting a more general origin in water's dynamics.
- Vibrational modes associated with the Boson peak are spatially extended and resemble transverse phonons from ice Ih.
Conclusions:
- The Boson peak in water arises from intrinsic liquid dynamics, specifically the emergence of low-density-like structures in the supercooled state.
- Confinement can influence, but does not solely cause, the Boson peak.
- The findings link the Boson peak to fundamental vibrational properties of water, connecting its liquid and solid (ice) phases.
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