Abstract
Using density functional theory, we investigated how substituting sulfur atoms for iron atoms affects the structure and energy of the body centered cubic and hexagonal close-packed iron phases at 350GPa and at 0K. We conclude that formation of random (Fe,S) solid solutions is energetically favorable in all intermediate compositions, although the random low-symmetry substitutions cause structural distortion. The (Fe,S) solid solution is nearly as favorable as the mechanical mixture of Fe-hcp and FeS-B2. This finding, in combination with dynamical stability, defines the B2 structure as a strong candidate for the sulfur-bearing phase of the Earth's inner core.