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Molecular dynamics of the water liquid-vapor interface
M A Wilson1, A Pohorille, L R Pratt
1Department of Chemistry, University of California, Berkeley 94720, USA.
The Journal of Physical Chemistry
|January 1, 1987
Summary
Molecular dynamics simulations reveal water molecule orientation at the liquid-vapor interface. Surface dipole density and hydrogen bonding are key factors influencing interfacial properties.
Area of Science:
- Physical Chemistry
- Computational Chemistry
Background:
- Understanding the liquid-vapor interface is crucial for various chemical and physical processes.
- Molecular simulations provide insights into interfacial phenomena at the molecular level.
Purpose of the Study:
- To investigate the equilibrium structure and properties of the water liquid-vapor interface using molecular dynamics.
- To analyze molecular orientation, hydrogen bonding, and electrical properties at the interface.
Main Methods:
- Molecular dynamics (MD) simulations were performed using the TIP4P model for water.
- Analysis included intermolecular pair potentials, molecular orientations, and hydrogen bond analysis.
Main Results:
- The average surface dipole density points from vapor to liquid.
- Water molecules at the interface exhibit broad orientational distributions, with the C2 nu axis often parallel to the interface.
- All near-neighbor molecules in the outermost layers are hydrogen-bonded.
- The mean electric field is parallel to the mean polarization.
- Calculated surface tension (132 +/- 46 dyn/cm) differs significantly from experimental values (68 dyn/cm at 325 K).
Conclusions:
- Water molecule orientation at the free surface differs from that near planar walls.
- Macroscopic descriptions of electrical properties require considering more than just dipolar charge distributions.
- The TIP4P model yields a surface tension value that deviates from experimental data for water.