Abstract

The vibrational density of states (VDOS) Overlap is widely expected to correlate positively with the interfacial thermal conductance (G), yet it fails to do so at numerous systems, and at gold/water interfaces, it actually decreases with increasing G. Here, we use non-equilibrium molecular dynamics simulations of numerous metal/water interfaces for a range of solid/liquid interaction strengths (ε_SL) to explain this contradiction. We show that the VDOS Overlap is a contingent metric: its trend with ε_SL depends on the relative positioning of the interfacial solid and liquid VDOS distributions, which is set by the extent of the bulk solid spectrum. By comparing the spectrally decomposed heat flux (SDHF) to the VDOS within each medium, we find that the degree to which the interfacial liquid utilises its available vibrational modes (η_IL) tracks the cross-metal hierarchy in G as closely as bulk-spectrum measures, while remaining invariant with ε_SL within each metal. An additional finding is that the bottleneck to cross-metal energy transport lies on the interfacial liquid side, not in the spectral similarity between the two media: η_IL matches the predictive power of the bulk-spectrum measures and additionally locates the limiting side of the interface, which a bulk-spectrum measure of the solid alone does not.