Deformation Potential for Shear Strains: Application to Copper

Simple and accurate expressions for the deformation potentials at symmetry points for shear strains are derived within the framework of the Green's function method. These formulas are applied to the strain-induced shifts of the energy levels of copper at $\Gamma$, $X$, and $L$ (including second-order effects when they are important), and the results are compared with the available data obtained from piezoreflectance measurements on single-crystal copper.