First principles study of the electronic and mechanical properties of a porous carbon

Carbon is a versatile element in the periodic table, which can form many allotropes with various properties in nature. In this work, the electronic and mechanical properties of a low energy porous carbon, a topological nodal line material, are studied by first principles method. Elastic and dynamical stabilities under hydrostatic pressure are investigated, which reveal that the dynamical instability occurs first. It is a material with negative linear compressibility along the a axis. Tension and compression strains are applied in different crystal orientations to obtain the corresponding stresses. The results indicate that the c axis can endure the smallest strains, the a axis can withstand moderate ones while the b axis can bear the largest ones, however, the resulted stresses have very different behaviors. Shear strains are exerted on different crystal planes to see the corresponding mechanical responses, which uncover that the (100)[010] shear pattern has the lowest critical stress than other shear patterns. The crystal structure, dynamical stability, and electron density difference under the critical strains are checked. The reasons for the different mechanical behaviors under pressure and strain are proposed. The effects of pressure and strain on its topological property are also studied.