Energy Loss Spectrum of Copper

The complex dielectric function ε (0,ω) of copper is calculated by a realistic band model up to \(\hbar\omega{=}25\) eV. the energy values ad the wave functions are calculated by APW method with the Chodorow potential. The eleven energy bands are used to obtain the matrix elements of the interband transitions. The energy loss spectrum at long wave limit is determined from the complex dielectric function. It has a broad peak whose center is situated near 20 eV. Since the plasmon energy of the electron gas of the same electron density as that of copper is about 10 eV, the observed energy loss spectrum is not free-electron like, but its character is ascribed to the interband transition from the 3d-bands to the empty bands. The observed energy loss spectrum by Takigawa et al. is in good agreement with the result of our calculation.