Ab initio x-ray absorption near-edge structure study of Ti K-edge in rutile.

This work reports a theoretical x-ray absorption near-edge structure (XANES) spectroscopy study at the Ti K-edge in TiO(2) rutile. We present detailed ab initio computations of the Ti K-edge XANES spectrum performed within the multiple-scattering framework. An extensive discussion is presented concerning the size of the cluster needed to reproduce the experimental spectrum, especially regarding the split main absorption line. In addition, the role of the exchange and correlation potential (ECP) in reproducing all the experimental XANES features is discussed. The best agreement between experimental data and computations is obtained by using real ECP potentials, i.e. the energy-dependent Dirac-Hara exchange potential, or by using only the real part of the energy-dependent Hedin-Lundqvist complex potential, together with an additional imaginary constant to account for the core-hole lifetime and the experimental resolution. The addition of the imaginary part of the HL potential worsens the agreement between the experimental and calculated spectra, indicating the failure of the complex part of the Hedin-Lundqvist ECP in accounting for the electron damping in these systems.