Thermal conductivity of diamond under extreme pressure: A first-principles study

Using a first-principles approach based on density functional perturbation theory and an exact numerical solution to the phonon Boltzmann equation, we show that application of high compressive hydrostatic pressure dramatically increases the thermal conductivity of diamond. We connect this enhancement to the overall increased frequency scale with pressure, which makes acoustic velocities higher and reduces phonon-phonon scattering rates. Of particular importance is the often-neglected fact that heat-carrying acoustic phonons are coupled through lattice anharmonicity to higher frequency optic modes. An increase in optic mode frequencies with pressure weakens this coupling and contributes to driving the diamond thermal conductivities to far larger values than in any material at ambient pressure and temperature.