Lattice dynamics and Raman spectrum of rutile TiO2: The role of soft phonon modes in pressure induced phase transition

Using the plane-wave pseudopotential technique based on the first-principles density functional perturbation theory (DFPT), we have studied the vibrational properties and Raman susceptibility tensor at ambient and high pressure of rutile phase of TiO2. Full phonon dispersion curves and phonon densities of states with projected phonon density of states and Raman tensors at high pressures are calculated and given. It is found that rutile TiO2 shows a pressure induced phase transition, especially when lattice dynamical instabilities are involved, like the soft phonon modes, at a hydrostatic pressure lower than 10 GPa. An analyses of the vibrational displacements is given. The possibility to use Raman line intensities as an additional tool in the study of phase transitions is also discussed.