Lower shear velocity of HCP-Fe under anisotropic stress from first-principles calculations

Abstract

Earth’s core consists of a solid inner core and a liquid outer core, composed primarily of iron. The pressure in the solid inner core is about 330 gigapascals (GPa) at the temperature close to the melting point. Considering the extensive experimental and theoretical data, the shear wave ([Formula: see text]-wave) velocity of the inner core is much lower than that of pure iron. Since the lower [Formula: see text]-wave velocity has been observed in the seismic models, reasons have been widely discussed such as the premelting of iron in the Earth’s inner core. In this paper, a new explanation is expected to be proposed under the anisotropic stress. The calculated longitudinal wave and [Formula: see text]-wave velocity of pure hexagonal close-packed iron (HCP-Fe) model based on the density functional theory (DFT) at the different density are matching with the seismic wave, the atomic distribution of HCP-Fe is obtained under the anisotropic stress. Unfortunately, it is unlikely conformed there was an inner-core condition due to the unreal anisotropic stress, although the lower [Formula: see text]-wave velocity is. Somehow, this lower [Formula: see text]-wave velocity may provide a new horizon to build mineralogical models for discussing. In addition, the [Formula: see text]-wave and viscosity of iron are strongly dependent on shear stress, we then give a mathematical equation between the [Formula: see text]-wave velocity and viscosity empirically by the shear behavior. It is revealed that the shear stress of iron has a positive influence on the [Formula: see text]-wave and viscosity.