We calculate an atomistically detailed free-energy profile across a heterogeneous system using a
nonequilibrium approach. The path-integral formulation of Crooks fluctuation theorem is used in
conjunction with the intrinsic sampling method (ISM) to calculate the free-energy profile for the
liquid-vapour interface of the Lennard-Jones fluid. Free-energy barriers are found corresponding
to the atomic layering in the liquid phase as well as a barrier associated with the presence of an
adsorbed layer as revealed by the intrinsic density profile. Our findings are in agreement with
profiles calculated using Widom’s potential distribution theorem applied to both the average and
the intrinsic profiles as well as literature values for the excess chemical potential.