First Principles Molecular Dynamics Simulations of molten (Mg,Fe)O at Mantle Conditions

Abstract:

Ferropericlase, (Mg,Fe)O, is thought to be the second most abundant component of the Earth's lower mantle. Because of its geological relevance, crystalline (Mg,Fe)O has been extensively studied to assess the effects of Fe on various seismically observable properties. However, the role of Fe in liquid phase remains mostly unknown. Recently, we have initiated the first-principles study of liquid (Mg,Fe)O over relevant broad ranges of pressure and temperature using local spin density approximation (LSDA). We also explore the use of generalized gradient approximation (GGA) and Hubbard (U) term. Our results on molten (Mg_0.83Fe_0.17)O show that for any isotherm the low spin (LS, non-magnetic) and the high spin (HS, magnetic) states have similar compressibility. They also predict the HS to LS transition occurring at much lower pressure of around 10 GPa, with transition pressure being positively correlated to temperature. These trends are generally consistent with the behavior shown by the solid phase. The calculated difference in enthalpy between the HS and LS remains small over wide pressure range indicating the possibility of coexistence of two spin states in the deep mantle melt.