Structure and Dynamics of the Instantaneous Water/Vapor Interface Revisited by Path-Integral and Ab-Initio Molecular Dynamics Simulations

TL;DR

This study uses advanced molecular dynamics simulations to analyze the structure and orientation of water molecules at the vapor interface, revealing layered arrangements and specific bond orientations.

Contribution

It introduces a combined use of path-integral and ab-initio simulations with an instantaneous surface definition to revisit water/vapor interface structure.

Findings

One OH bond points out of water into vapor phase.

An additional layer of water molecules aligns parallel to the surface.

Orientation of the second layer is reversed compared to the topmost layer.

Abstract

The structure and dynamics of the water/vapor interface is revisited by means of path-integral and second-generation Car-Parrinello ab-initio molecular dynamics simulations in conjunction with an instantaneous surface definition [A. P. Willard and D. Chandler, J. Phys. Chem. B 114, 1954 (2010)]. In agreement with previous studies, we find that one of the OH bonds of the water molecules in the topmost layer is pointing out of the water into the vapor phase, while the orientation of the underlying layer is reversed. Therebetween, an additional water layer is detected, where the molecules are aligned parallel to the instantaneous water surface.