Thermodynamics of spin crossover in ferropericlase: an improved LDA+$U_{sc}$ calculation

Abstract

We present LDA+$U_{sc}$ calculations of high-spin (HS) and low-spin (LS) states in ferropericlase (fp) with an iron concentration of 18.75$\%$. The Hubbard parameter $U$ is determined self-consistently with structures optimized at arbitrary pressures. We confirm a strong dependence of $U$ on the pressure and spin state. Static calculations confirm that the antiferromagnetic configuration is more stable than the ferromagnetic one in the HS state, consistent with low-temperature measurements. Phonon calculations guarantee the dynamical stability of HS and LS states throughout the pressure range of the Earth mantle. Compression curves for HS and LS states agree well with experiments. Using a non-ideal mixing model for the HS to LS states solid solution, we obtain a crossover starting at $\sim$45 GPa at room temperature and considerably broader than previous results. The spin-crossover phase diagram is calculated, including vibrational, magnetic, electronic, and non-ideal HS-LS entropic contributions. Our results suggest the mixed-spin state predominates in fp in most of the lower mantle.

8 pages, 8 figures

References in corpus (7)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Advanced capabilities for materials modelling with Quantum ESPRESSO
• Density functional theory in transition-metal chemistry: a self-consistent Hubbard U approach
• Hubbard-corrected density functional perturbation theory with ultrasoft pseudopotentials
• LDA+Usc calculations of phase relations in FeO
• Thermodynamic properties of ε-Fe with thermal electronic excitation effects on vibrational spectra
• Phonon dispersions throughout the iron spin crossover in ferropericlase

Cited by in corpus (1)

• Thermodynamics and its Prediction and CALPHAD Modeling: Review, State of the Art, and Perspectives