Nonmonotonic heat transport in pressurized hydrogen-loaded hydroquinone clathrate

Pressure-dependent heat conduction in flexible molecular solids is governed by coupled changes in density, anisotropy, energy-current correlations, and vibrational dynamics. Here, we quantify these effects in singly occupied H 2 @ β -hydroquinone clathrate using equilibrium molecular dynamics at 270 K over 10 −4 to 25 GPa. Directional Green–Kubo calculations based on 50 non-overlapping 500 ps blocks per state show that the orientationally averaged thermal conductivity remains 0.43–0.56 W/(m·K) below 1.0 GPa, increases to 1.15 W/(m·K) at 5.0 GPa and 1.65 W/(m·K) at 10 GPa, and decreases by 25% to 1.24 W/(m·K) at 25 GPa. The initial rise accompanies strong contraction along the short cell axis, whereas the decrease follows reconstruction-like strain redistribution and occurs despite continued densification. Heat-current decomposition attributes the enhancement to the hydroquinone framework; the H 2 self-term decreases continuously and the host-guest cross contribution remains small. PDOS, SED, effective peak-lifetime, participation-ratio, and localization analyses show that pressure strengthens and reconnects low-frequency framework vibrations. The conductivity maximum occurs while the effective peak lifetimes shorten, indicating that more strongly dispersive low-frequency features and connected framework pathways, rather than lifetime extension, accompany the transport enhancement. The results provide a statistically resolved microscopic mechanism for nonmonotonic heat transfer in a pressure-responsive host-guest solid.