Liquid iron alloys at outer core conditions by first-principles calculation

Since the density of the outer core deduced from seismic data is about 10% lower than that of pure iron at core pressures and temperatures (P-T), it is widely believed that the outer core includes one or more light elements. The light element in the core, however, has not yet been identified. Comparison of the density and sound velocity of liquid iron alloys with observations, such as the PREM, is a promising way to determine the species and quantity of light alloying component(s) in the outer core. Here we report the results of a first-principles molecular dynamics study on liquid iron alloyed with different concentrations of sulfur and hydrogen, in order to understand the effects of these impurities on the liquid density and sound velocity under outer core P-T conditions. We discuss the composition of the Earth’s outer core based on a comparison of the present results with the PREM density and velocity profiles.