Intrinsic fluid interfaces and nonlocality

We present results of an extensive molecular dynamics simulation of the structure and fluctuations of a liquid-gas interface, close to its triple point, in a system with cutoff Lennard-Jones interactions. The equilibrium density profile, averaged and (shape dependent) constrained intrinsic density profiles together with the fluctuations of the interfacial shape are extracted using an intrinsic sampling method. The correlation between fluctuations in the interfacial shape and in the intrinsic density show that the latter is not due to rigid translations of some underlying profile, as is most commonly assumed. Instead, over the whole range of wavelengths from the system size down to the molecular diameter, we see wave-vector dependent behavior in good agreement with a nonlocal interfacial Hamiltonian theory specifying the shape dependence of the intrinsic profilesA. O. P. acknowledges the support of the bank of Santander and UCIIIM for a Chair of Excellence. E. M. F., E. C., P. T., and C. R. acknowledge support from grants MODELICO (Comunidad de Madrid) and FIS2010- 22047-C05 (Ministerio de Educación y Ciencia