Lattice dynamics calculations for ferropericlase with internally consistent LDA+U method

Abstract

Vibrational densities of states and phonon dispersion relations for Mg 0.875Fe0.125O ferropericlase in the high-and low-spin (HS and LS) states were calculated from first principles lattice dynamics using the internally consistent LDA+U technique. Finite-temperature thermodynamic properties were determined based on the quasi-harmonic approximation including the HS and LS mixing entropy and the magnetic entropy effects, which gave pressure and temperature variations of the low-spin fraction. Our results suggest that for thermodynamic modeling of the earth's interior, the effect of the mixed spin state cannot be ignored in the lower mantle, especially the lowermost part. The anomaly in the seismic wave velocity due to the spin crossover transition of ferropericlase, if it exists, is difficult to detect because of the wide pressure range of the transition, which is broadened by the temperature effect and the damping of the amplitude of the slow seismic wave. © 2012. American Geophysical Union. All Rights Reserved.