First principles simulations of liquid Fe-S under Earth's core conditions

TL;DR

This study uses first principles simulations to investigate how sulfur impurities affect the structural, electronic, and dynamical properties of liquid iron-sulfur alloy under Earth's core conditions, finding negligible impact on viscosity.

Contribution

It provides the first detailed electronic structure analysis of liquid Fe-S alloy at Earth's core conditions, highlighting sulfur's structural role and its minimal effect on viscosity.

Findings

Sulfur impurities do not promote polymerization in liquid Fe-S.

Sulfur causes a net S-S repulsion explained by electronic structure.

Sulfur impurities have negligible effect on liquid core viscosity.

Abstract

First principles electronic structure calculations, based upon density functional theory within the generalized gradient approximation and ultra-soft Vanderbilt pseudopotentials, have been used to simulate a liquid alloy of iron and sulfur at Earth's core conditions. We have used a sulfur concentration of $\approx 12 % $wt, in line with the maximum recent estimates of the sulfur abundance in the Earth's outer core. The analysis of the structural, dynamical and electronic structure properties has been used to report on the effect of the sulfur impurities on the behavior of the liquid. Although pure sulfur is known to form chains in the liquid phase, we have not found any tendency towards polymerization in our liquid simulation. Rather, a net S-S repulsion is evident, and we propose an explanation for this effect in terms of the electronic structure. The inspection of the dynamical properties of the system suggests that the sulfur impurities have a negligible effect on the viscosity of Earth's liquid core.