Ideal strengths and bonding properties of PuO2 under tension

We perform a first-principles computational tensile test on PuO$_{2}$ based on density-functional theory within local density approximation (LDA)+\emph{U} formalism to investigate its structural, mechanical, magnetic, and intrinsic bonding properties in the four representative directions: [001], [100], [110], and [111]. The stress-strain relations show that the ideal tensile strengths in the four directions are 81.2, 80.5, 28.3, and 16.8 GPa at strains of 0.36, 0.36, 0.22, and 0.18, respectively. The [001] and [100] directions are prominently stronger than other two directions since that more Pu$-$O bonds participate in the pulling process. Through charge and density of states analysis along the [001] direction, we find that the strong mixed ionic/covalent character of Pu$-$O bond is weakened by tensile strain and PuO$_{2}$ will exhibit an insulator-to-metal transition after tensile stress exceeds about 79 GPa.