Examination of inconsistencies in the physical modeling of vapor–liquid interfaces of strongly non-ideal mixtures

The accurate modeling of fluid interfaces is crucial in numerous scientific and engineering applications. Different physical models such as molecular simulation (MS), density functional theory (DFT), and density gradient theory (DGT) are usually employed for this purpose. However, recent findings have highlighted discrepancies in interfacial structure predictions, particularly for strongly non-ideal azeotropic systems [<i>Fluid Phase Equilib.</i>, 2023, <b>564</b>, 113596]. Specifically, DGT was observed to produce spurious interfacial profiles that deviated significantly from those obtained from MS. This study systematically investigates these inconsistencies by performing a comparative in depth analysis of MS, DFT, and DGT for eight binary alkane + alcohol azeotropic systems. The unusual topology of the interfacial structure is confirmed by all three methods, although important quantitative differences are observed. Possible reasons for these inconsistencies are discussed.