Local field effects in the electron energy loss spectra of rutile TiO2.

We present an ab initio calculation of the electron energy loss spectrum of rutile TiO2 in the energy range of 0 to 60 eV, focusing our interest on the excitation from the titanium 3p semicore levels. The results are compared to our measurements. Local field effects turn out to be crucial at those energies, and their inclusion in the calculation yields excellent agreement between theory and experiment. We show how in rutile these effects induce an anisotropy in the otherwise isotropic transitions from quasispherical 3p semicore states to 3d states of almost cubic symmetry.