Surface Tension of Ab Initio Liquid Water at the Water-Air Interface

TL;DR

This study uses ab initio molecular dynamics to accurately calculate the water-air surface tension, emphasizing the importance of basis set choice and van der Waals corrections for realistic results.

Contribution

It demonstrates the critical impact of basis sets and van der Waals corrections on AIMD surface tension calculations, providing benchmarks for future simulations.

Findings

Triple and quadruple-ξ basis sets yield similar, accurate surface tension results.

Van der Waals corrections significantly influence the calculated surface tension.

Surface tension is insensitive to exchange-correlation functional details.

Abstract

We report calculations of the surface tension of the water-air interface using ab initio molecular dynamics (AIMD) simulations. We investigate the simulation cell size dependence of the surface tension of water from force field molecular dynamics (MD) simulations, which show that the calculated surface tension increases with increasing simulation cell size, thereby illustrating that a correction for finite size effects is required for the small system used in the AIMD simulation. The AIMD simulations reveal that the double-{\xi} basis set overestimates the experimentally measured surface tension due to the Pulay stress, while the triple and quadruple-{\xi} basis sets give similar results. We further demonstrate that the van der Waals corrections critically affect the surface tension. AIMD simulations without the van der Waals correction substantially underestimate the surface tension, while van der Waals correction with the Grimme's D2 technique results in the value for the surface tension that is too high. The Grimme's D3 van der Waals correction provides a surface tension close to the experimental value. Whereas the specific choices for the van der Waals correction and basis sets critically affect the calculated surface tension, the surface tension is remarkably insensitive to the details of the exchange and correlation functionals, which highlights the impact of long-range interactions on the surface tension. These simulated values provide important benchmarks, both for improving van der Waals corrections, and AIMD simulations of aqueous interfaces.