Vibrational and thermodynamic properties of wadsleyite: A density functional study

The vibrational properties of Mg2SiO4 wadsleyite have been calculated over a wide pressure range using density functional perturbation theory (DFPT). Both the normal mode frequencies and their volume dependences are consistent with the available Raman and infrared data. We provide detailed information about vibrational properties that are still not experimentally available. The vibrational density of states (vDOS) is used to calculate the Helmholtz free energy within the quasi-harmonic approximation (QHA) and other thermodynamic quantities without further approximations. The extensive and successful comparisons with experiments demonstrate once more that the QHA combined with first principles vDOSs can provide accurate thermodynamic properties of minerals over the large pressure-temperature regime relevant for the Earth.