Ab initio approach to the excited electron dynamics in rutile and anatase TiO2.

The relaxation of excited electrons in the conduction band of titanium dioxide with the rutile and anatase structure is investigated by means of a first-principle method. The evaluations are based on the pseudo-potential plane-wave approach to the electronic band structure calculations, the density-functional perturbation theory for the calculations of phonons and electron-phonon interactions, and on the 'Fermi golden rule' for evaluations of the electron relaxation time and the energy loss time. We demonstrate two regimes of the electron relaxation. For the excited electrons with energy less than 0.01 eV above the conduction band bottom the relaxation occurs in the pico-second timescale, whereas at higher excitation energies the electron relaxation time is within a few femto-seconds and the energy loss time is within a few tens of femto-seconds.