Ideal strength of diamond, Si, and Ge

We have calculated the ideal shear strength and ideal tensile strength of C, Si, and Ge in the diamond structure. We find ideal shear strengths of 95 GPa, 6.5 GPa. and 4.5 GPa, and ideal tensile strengths of 95 GPa. 23 GPa, and 14 GPa for C, Si and Ge respectively. The shear calculation is performed on the {111} slip plane sheared in a < 112 > direction, and the tensile load is applied in the < 111 > direction. We allowed for a full relaxation of the strains orthogonal to the applied strain as well as the atomic basis vectors.