We report density functional theory (DFT) results for the shear stresses of uniaxially compressed diamond under conditions corresponding to strong shock wave compression. A nonmonotonic dependence of shear stresses on uniaxial strain was discovered in all three low-index crystallographic directions: , , and . For compression the shear stress even becomes negative in the region near the minimum of the shear stress-strain curve. The DFT results suggest that anomalous elastic regime observed in recent molecular dynamics shock simulations is a real phenomenon caused by a significant delay or even freezing of the plastic response
