The inverse-power soft-sphere model provides a controlled platform for tuning the range and softness of purely repulsive interparticle interactions through the exponent $n$, with the hard-sphere limit recovered as $n\to \infty$. While the bulk thermodynamics and solid-liquid interfacial free energies of this model system have been extensively characterized, the corresponding excess interfacial stress and its dependence on interaction softness remain largely unexplored. In this work we perform molecular dynamics simulations to quantify the reference excess interfacial stress ${\tau }_1$ of equilibrium face-centered-cubic soft-sphere solid-liquid interfaces for the (100), (110), and (111) orientations over a broad range of inverse-power exponents, $n=6–100$, together with a model-dependent continuation of the finite-$n$ branch to $s=1/n=0$. Here the subscript 1 denotes quantities evaluated at the reference coexistence state $T_{\mathrm{m}}^{*}=1$, from which values along the corresponding coexistence line can be generated by inverse-power scaling. The pressure tensor profiles reveal that the normal component remains consistent with mechanical equilibrium in the bulk phases, whereas the lateral pressure components exhibit pronounced orientation- and softness-dependent redistribution in the interfacial region. As a result, ${\tau }_1$ displays a much stronger dependence on $1/n$ and crystallographic orientation than the reference solid-liquid interfacial free energy ${\gamma }_1$. In particular, ${\tau }_1$ changes sign for the (100) orientation as the repulsion becomes steeper, whereas the (110) and (111) interfaces remain predominantly compressive and become increasingly negative toward the hard-sphere side. After removing the solid-density area scale $k_{\mathrm{B}}T{\rho }_{\mathrm{s}}^{2/3}$, the softness dependence of ${\gamma }_1$ is substantially reorganized, whereas the stress sign reversal and the increasingly compressive (110) and (111) trends persist. This density-scaled comparison shows that the principal stress trends arise from interfacial stress redistribution rather than from the change in bulk density alone. By combining the present stress data with the benchmark interfacial free energies ${\gamma }_1$ of Davidchack and Laird [Phys. Rev. Lett. 94, 086102 (2005)], we further form cross-study reference combinations ${\tau }_1-{\gamma }_1$, which are negative for all orientations and substantially more anisotropic than ${\gamma }_1$ itself. These results provide a softness-resolved benchmark for interfacial thermodynamics in a purely repulsive model system and establish excess interfacial stress as a sensitive mechanical probe of solid-liquid interfacial structure beyond the interfacial free energy alone.

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• Interface & surface thermodynamics
• Stress
• Surface & interfacial phenomena
• Soft colloids
• Solid-solid interfaces
• Molecular dynamics