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

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 [Willard, A. P.; Chandler, D. J. Phys. Chem. B 2010, 114, 1954]. 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.

On the complex structural diffusion of proton holes in nanoconfined alkaline solutions within slit pores

“…However, importantly, the O*H′ bond of the nascent water molecule is a ‘dangling' OH bond (also called free OH or single-donor species), which is one out of several ideal hydrogen bond arrangements that can terminate planar water interfaces38. Indeed, there is now solid evidence accumulated that the preferred termination of the water surface in contact with vapour occurs via such dangling OH bonds, which implies that these water molecules donate only a single hydrogen bond towards the interior39. This is exactly the situation met in the centre panel of Fig.…”

Orientation‐Induced Adsorption of Hydrated Protons at the Air–Water Interface

“…[1] At the air-water interface, a concordant H 2 O orientation has been reported earlier using classical and ab initio simulations. [22] As the formation of hydrogen bonds in water depends on the relative orientation of the OH bonds, we used the dipole energy of the oriented H 3 O + in the z-dependent interfacial electric field E z (z), caused by the oriented water molecules, as a proxy for the hydrogen-bonding capability. The sign of E z (z) (Figure 4 B, right inset) is in agreement with the results from the ab initio simulations, taking into account that ions only probe the space between the water molecules.…”

The Surface Activity of the Hydrated Proton Is Substantially Higher than That of the Hydroxide Ion

“…[16] As D 3 O + is av ery weak hydrogen-bond acceptor, [8b] it prefers to stay close to the surface [15,17] where the number of neighboring species to make ah ydrogen bond with, specifically at the immediate water-air interface,i sn aturally scarce. [18] However,t he most recent multistate empirical valence bond model-based calculation comparing the instantaneous airwater interfacial structure and the Gibbs dividing surface shows that also the second solvation shell structure can influence surface affinity. [17] Thef ree energy minimum very close to the interface ( % 1 )i ss imilar for hydrated proton and hydroxide.H owever,t he hydroxide has ah igher maximum in free energy than the hydrated proton at 2-3 away from the instantaneous surface,i ncreasing the barrier for hydroxide to come to the interface.…”