Elasticity and mechanical instabilities of diamond at megabar stresses: Implications for diamond-anvil-cell research

We present first-principles calculations of the stress–strain curves for diamond under nonhydrostatic tetragonal compression, in the regime of operation of diamond-anvil cells (DACs). We provide a parametrization of the stress components as a function of strain, which is potentially useful for the controlled design of DACs. A stability analysis shows that a tetragonal-shear mechanical instability sets in in diamond when σz−σr=200 GPa, where σz and σr are the axial and radial components of the stress, respectively.