Thermoelastic properties of ringwoodite (Fex,Mg1−x)2SiO4: Its relationship to the 520 km seismic discontinuity

We combine density functional theory (DFT) within the local density approximation (LDA), the quasiharmonic approximation (QHA), and a model vibrational density of states (VDoS) to calculate elastic moduli and sound velocities of γ-(Fex,Mg1−x)2SiO4γ-(Fex,Mg1−x)2SiO4 (ringwoodite), the most abundant mineral of the lower Earth's transition zone (TZ). Comparison with experimental values at room-temperature and high pressure or ambient-pressure and high temperature shows good agreement with our first-principles findings. Then, we investigate the contrasts associated with the β→γ(Fex,Mg1−x)2SiO4β→γ(Fex,Mg1−x)2SiO4 transformation at pressures and temperatures relevant to the TZ. This information offers clearly defined reference values to advance the understanding of the nature of the 520 km seismic discontinuity.