The particle-in-cell model for ab initio thermodynamics: implications for the elastic anisotropy of the Earth's inner core

Abstract

We assess the quantitative accuracy of the particle-in-cell (PIC) approximation used in recent ab initio predictions of the thermodynamic properties of hexagonal-close-packed iron at the conditions of the Earth's inner core. The assessment is made by comparing PIC predictions for a range of thermodynamic properties with the results of more exact calculations that avoid the PIC approximation. It is shown that PIC gives very accurate results for some properties, but that it gives an incorrect treatment of anharmonic lattice vibrations. In addition, our assessment does not support recent PIC-based predictions that the hexagonal c/a ratio increases strongly with increasing temperature, and we point out that this casts doubt on a proposed re-interpretation of the elastic anisotropy of the inner core.

25 pages, 9 figures, submitted to Physics of the Earth and Planetary Interiors

References in corpus (3)

• Iron under Earth's core conditions: Liquid-state thermodynamics and high-pressure melting curve
• The elastic constants of MgSiO3 perovskite at pressures and temperatures of the Earth's mantle
• High Pressure Thermoelasticity of Body-centered Cubic Tantalum

Cited by in corpus (5)

• Thermal properties of materials from ab-initio quasi-harmonic phonons
• First-principles thermal equation of state and thermoelasticity of hcp Fe at high pressures
• Lattice dynamics and thermodynamics of bcc iron at pressure: first-principles linear response study
• The axial ratio of hcp iron at the conditions of the Earth's inner core
• Thermal effects on lattice strain in hcp Fe under pressure