Enhanced wavelength-dependent surface tension of liquid-vapour interfaces

Due to the simultaneous presence of bulk-like and interfacial fluctuations the understanding of the structure of liquid-vapour interfaces poses a long-lasting and ongoing challenge for experiments, theory, and simulations. We provide a new analysis of this topic by combining high-quality simulation data for Lennard-Jones fluids with an unambiguous definition of the wavenumber-dependent surface tension $\gamma(q)$ based on the two-point correlation function of the fluid. Upon raising the temperature, $\gamma(q)$ develops a maximum at short wavelengths. We compare these results with predictions from density functional theory. Our analysis has repercussions for the interpretation of grazing-incidence small-angle X-ray scattering (GISAXS) at liquid interfaces.