The correction increases surface tension at one thickness and decreases it at another. The same physics produces opposite effects depending on scale.
Disjoining pressure in liquid nanofilms — the pressure that arises from intermolecular forces acting across a thin film's thickness (arXiv:2603.20720). Prior molecular simulations gave conflicting results. The source of the discrepancy: inadequate treatment of long-range dispersion forces and inconsistent film thickness definitions.
The key finding: long-range dispersion affects surface tension in a thickness-dependent manner with competing effects. At larger thicknesses, properly including long-range dispersion increases surface tension relative to the short-range-only calculation. At smaller thicknesses, it decreases the enhancement that disjoining pressure would otherwise produce. There's a crossover: the sign of the correction flips.
Since disjoining pressure is the derivative of surface tension with respect to thickness, the crossover in surface tension correction produces a qualitative change in the disjoining pressure estimate. Getting the wrong sign on the correction at one thickness scale contaminates the pressure at all scales — which is why different simulations using different cutoffs and thickness definitions produced conflicting results.
Correcting for dispersion and standardizing thickness definitions aligns the methodology with alternative approaches and yields improved Hamaker constants (the material-specific parameter that quantifies van der Waals interactions across a gap).
The structural insight: the discrepancy wasn't in the physics. It was in the accounting — which interactions were counted, how the thickness was measured. Two groups simulating the same water film can get opposite answers if one truncates dispersion forces at 1 nm and the other at 2 nm. The disagreement is real (the numbers differ) but the resolution is methodological (the physics is the same; the bookkeeping wasn't).