Ideal strengths, structure transitions, and bonding properties of a ZnO single crystal under tension

We perform a first-principles computational tensile test (FPCTT) on a ZnO single crystal based on density functional theory to systematically investigate structural transitions, mechanical, and intrinsic bonding properties in the three representative directions, [Formula: see text], [0001], and [Formula: see text]. Stress as a function of tensile strain shows that the ideal tensile strengths in the three directions are 16.2 GPa, 22.4 GPa, and 19.0 GPa, corresponding to strains of 0.20, 0.16, and 0.16, respectively. The [0001] is the strongest direction due to the strongest bonding between the most closely packed Zn and O(0001) layers. We demonstrate that different structures in these three directions lead to different structural transitions, i.e. from a wurtzite (WZ) to a body-centered tetragonal (BCT) structure for [Formula: see text], to a graphite-like (GP-like) structure for [0001], and to a quasi-hexagonal (quasi-HX) structure for [Formula: see text], respectively. Bond length and charge density evolution under tension indicate the occurrence of bond formation and disassociation during these structure transitions. New O-Zn bonds form in the WZ [Formula: see text] BCT and WZ [Formula: see text] quasi-HX transitions, and the original O-Zn bonds break in the WZ [Formula: see text] GP-like transition.