Vibrational and thermodynamic properties of forsterite at mantle conditions

Vibrational and thermodynamic properties of forsterite at mantle conditions Li Li , Renata M. Wentzcovitch, Donald J. Weidner, Cesar R. S. Da Silva 1. Department of Geosciences, Mineral Physics Institute, Stony Brook University, Stony Brook, NY, 11790, USA 2. Department of Chemical Engineering and Materials Science, Minnesota Supercomputing Institute for Digital Technology and Advanced Computations, University of Minnesota, 421 Washington Avenue SE, Minnespolis, MN, 55455, USA Abstract We present a first principle study of the vibrational and thermodynamic properties of Mg2SiO4 forsterite up to 20 GPa. The calculated LDA frequencies and their pressure dependence are in good agreement with the available Raman and infrared spectroscopy data. We also predict the pressure dependence of the modes which are yet to be measured. Thermodynamic properties are obtained using the quasiharmonic approximation (QHA) to the free energy in conjunction with these results. The calculated P-V-T relations and thermodynamic properties agree well with the reported experimental data within the regime of validity of the QHA. The only discrepancies with experimental data that point out to intrinsic anharmonic effects are the mode Gruneisen parameters of 2 Raman and one infrared mode. However, their effect on thermodynamic properties appears to be negligible.