A DFT investigation of the electronic, optical, and thermoelectric properties of pentadiamond

Enhanced Hydrogen Storage Capacity in Two-Dimensional Fullerene Networks

In contrast to isolated C60 molecular dispersion in solvents, the monolayer C60 networks synthesized by Hou et al. (Nature 2022, 606, 507-510) feature compact nanocages, serving as natural containers for hydrogen storage. The anisotropic lattice and intrinsic local strains induce delocalization of conjugated π orbitals within C60, enabling hydrogen chemisorption without an additional chemical modification. Through first-principles calculations and molecular dynamics simulations, we reveal the correspondence between chemisorption sites and orbital distributions, determining the orientation of polyhedrons formed by physiosorbed hydrogen molecules. The combination of chemisorption and physisorption processes significantly enhances hydrogen storage capacity in monolayer C60 networks while maintaining the thermodynamic stability of the nanocage structures. Numerical results indicate a maximum internal hydrogen pressure exceeding 116 GPa at room temperature and atmospheric pressure. These findings suggest that monolayer C60 networks are promising solid-state candidates for highly efficient hydrogen storage.

Unexpected low thermal expansion coefficients of pentadiamond

A new carbon allotrope, pentadiamond, was recently reported in the literature. Herein, we investigate its thermal expansion and thermoelastic properties by first principles. It is observed that the bulk modulus and hardness of pentadiamond are far less than those of diamond, but the thermal expansion of pentadiamond is lower than that of diamond in the range of 0 K to 2000 K, and even negative in the temperature range of 0-190 K. The negative thermal expansion at low temperature originates from the transverse vibrations of the edge-shared atoms in the coplanar double-pentagon. The low thermal expansion at high temperature is contributed by the strong bonds in pentadiamond. Benefiting from the low thermal expansion, the elastic constants of pentadiamond decrease very slowly with respect to temperature compared with those of diamond. The low sensitivity of thermodynamic and thermoelastic properties to temperature makes pentadiamond a promising material for high anti-thermal-shock and accurate electronic device applications.