Divergence of the Thermal Conductivity in Uniaxially Strained Graphene

We investigate the effect of strain and isotopic disorder on thermal transport in suspended graphene by equilibrium molecular dynamics simulations. We show that the thermal conductivity of unstrained graphene, calculated from the fluctuations of the heat current at equilibrium is finite and converges with size at finite temperature. In contrast, the thermal conductivity of strained graphene diverges logarithmically with the size of the models, when strain exceeds a relatively large threshold value of 2%. An analysis of phonon populations and lifetimes explains the divergence of the thermal conductivity as a consequence of changes in the occupation of low-frequency out-of-plane phonons and an increase in their lifetimes due to strain.Comment: 6 pages, 7 figures. Accepted for publication in Physical Review

First-principles investigation of electronic, optical, mechanical and heat transport properties of pentadiamond: A comparison with diamond

Pentadiamond is a carbon allotrope consisting of hybrid sp2 and sp3 atoms, which has been predicted to be stable and synthesizable. In this work we employ first-principles calculations to explore the electronic structure, optical characteristics, mechanical response and lattice thermal conductivity of pentadiamond, performing a direct comparison with the corresponding properties in diamond. The HSE06 density functional predicts indirect electronic band gaps for pentadiamond and diamond with values of 3.58 eV and 5.27 eV, respectively. Results for optical characteristics reveal pentadiamond's large absorption in the middle UV region, where diamond does not absorb light, consistent with the smaller band gap of pentadiamond. The elastic modulus and tensile strength of pentadiamond are found to be 496 GPa and 60 GPa, respectively, considerably lower than the corresponding values for diamond. The lattice thermal conductivity is examined by solving the Boltzmann transport equation, with anharmonic force constants evaluated via state-of-the-art machine-learning interatomic potentials. We predict a thermal conductivity of 427 W/m-K for pentadiamond, less than one fifth of the corresponding quantity for diamond. Our results provide a useful vision of the intrinsic properties of pentadiamond, but also highlight some of its disadvantages in mechanical strength and heat conduction when compared to diamond