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

• Published in: Journal of Geophysical Research: Solid Earth Vol. 117; no. B12
• Main Authors: Fukui, Hiroshi, Tsuchiya, Taku, Baron, Alfred Q. R.
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 01-12-2012; American Geophysical Union
• Subjects: Earth sciences; Earth, ocean, space; elastic wave velocity; Entropy; Exact sciences and technology; ferropericlase; Geophysics; LDA+U; Lower mantle; Materials elasticity; Materials science; Seismic waves; spin crossover transition; thermodynamic properties; Thermodynamics; Wave velocity; density; lower mantle; mixing; Dispersion relation; Temperature effect; thermodynamics; thermodynamic properties; damping; pressure; anomalies; Modeling; Earth; amplitude; entropy; harmonics; Phonon dispersion; Lattice dynamics; temperature; Wave velocity; Spin state; seismic waves
• ISSN: 0148-0227; 2169-9313; 2156-2202; 2169-9356
• DOI: 10.1029/2012JB009591

Vibrational densities of states and phonon dispersion relations for Mg0.875Fe0.125O ferropericlase in the high‐ and low‐spin (HS and LS) states were calculated from first principles lattice dynamics using the internally consistent LDA+Utechnique. 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.
Key Points
The effect of the mixed spin state cannot be ignored to model the lower mantle
Anomaly in transverse velocity is related to phonon softening of the HS‐fp