Figure 1
From: Viscosity of hcp iron at Earth’s inner core conditions from density functional theory
Defect energetics as a function of pressure from first-principles calculations. (a) Vacancy formation enthalpy at static temperature for bcc (red), fcc (blue) and hcp (green) iron. The red dotted line represents extrapolation of the vacancy formation enthalpy of bcc iron at high pressure. A formation enthalpy of 0 eV is expected at ~240 GPa, comparable to the pressure corresponding to the tetragonal shear instability of bcc iron26. (b) Vacancy migration enthalpy of bcc (red), fcc (blue) and hcp (green) iron at static temperature. The inset shows the migration enthalpies of in-basal \(({{\rm{a}}}_{\parallel })\) and out-basal \(({{\rm{c}}}_{\parallel })\) plane migration in hcp Fe. (c) The activation energy ΔH = ΔHf + ΔHm of self-diffusion in fcc (blue) and hcp (green) Fe at static temperature. The slope corresponds to the activation volume \({V}_{A}=\partial H/\partial P\) for vacancy diffusion. The VA within the pressure regimes 120 > P > 240 GPa are indicated where ΔH varies almost linearly with P. In those regimes, the VA is obtained by a least-squares regression of our data.
