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Low lattice thermal conductivity of pentadiamond

The lattice thermal conductivity of carbon materials is particularly interesting because it can vary within a range spanning five orders of magnitude depending on the atomic configuration. Herein, we systematically study the lattice thermal conductivity and phonon transport properties of pentadiamond, a new three-dimensional carbon allotrope consisting of pentagonal carbon rings. Based on first-principles calculations and an iterative solution to the linearized Boltzmann transport equation, the intrinsic lattice thermal conductivity (kl) is found to be 490.88 W/mK at room temperature, much lower than 2664.93 W/mK of diamond. A detailed analysis of both harmonic and anharmonic properties reveals that the low kl of pentadiamond essentially originates from its large phonon phase space, short phonon relaxation time resulting from strong overlap between the acoustic and low-lying optical phonon branches, and the low phonon group velocity. The distinct thermal transport behavior exhibited in pentadiamond further shows the diversity and complexity in lattice thermal conductivity of carbon allotropes.