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Clusters of mobile molecules in supercooled water
Nicolas Giovambattista1, Sergey V Buldyrev, H Eugene Stanley
1Center for Polymer Studies and Department of Physics, Boston University, Massachusetts 02215, USA.
Summary
Mobile water molecules form clusters that grow and compact as temperature drops. This cooperative motion, observed in simulations, may explain liquid dynamics and relates to configurational entropy.
Area of Science:
- Physical Chemistry
- Computational Physics
- Materials Science
Background:
- Understanding water's complex dynamics is crucial for various scientific fields.
- Heterogeneous dynamics in liquids, especially water, remain a key area of research.
- Molecular dynamics simulations offer insights into microscopic liquid behavior.
Purpose of the Study:
- To investigate spatially heterogeneous dynamics in water using molecular dynamics.
- To identify and characterize clusters of mobile molecules and their properties.
- To explore the relationship between cluster characteristics and configurational entropy.
Main Methods:
- Extended Simple Point Charge (SPC/E) potential for water simulations.
- Molecular dynamics simulations to analyze molecular motion and clustering.
- Analysis of cluster size, compactness, correlation length, and fractal dimension.
Main Results:
- Mobile molecule clusters grow larger and more compact as temperature decreases.
- Cluster properties exhibit a fractal dimension similar to lattice animals.
- Cluster size and correlation length show a weak dependence on 1/S(conf).
- A linear relationship between cluster mass and 1/S(conf) suggests a link to cooperatively rearranging regions.
Conclusions:
- Stringlike cooperative motion within clusters may be a general mechanism for molecular rearrangement in liquids.
- Mobile molecule clusters in equilibrium and inherent structures differ on short timescales but converge on longer, diffusive timescales.
- The findings support the Adam-Gibbs approach to supercooled liquid dynamics.