Iron is one of the most abundant non-volatile elements in the solar system. As a major component of planetary metallic alloys, its immiscibility with silicates plays a major role in planetary formation and differentiation. Information about these processes can be gained by studying the equilibrium Fe isotope fractionation between metal alloys and molten silicates at conditions of core formation. In particular, recent attention has been paid to ⁵⁶Fe/⁵⁴Fe equilibrium isotope fractionation at conditions relevant to Earth's core formation and the influence that light elements (O, H, C, Ni, Si and S) have had in this process. Most of these experimental studies relied on the measurement of Fe isotope fractionation from quenched phases of silicate melts and molten iron alloys. The experimental works are extremely challenging, and may suffer different drawbacks. To overcome this, we use ab-initio computational methods to perform a systematic study of the ⁵⁶Fe/⁵⁴Fe equilibrium isotope fractionation in molten and solid Fe_1−xS_x alloys at conditions of the core formation (60 GPa, 3000 K). We show for the first time, that equilibrium isotope fractionation factors from solid systems can be used as proxies for molten systems with differences between these two methods less than 0.01‰ at the relevant P-T conditions. Additionally, we discuss the effect of sulphur concentration on the equilibrium Fe isotope fractionation and show that although there are some structural changes due to atom substitutions, the wide range of studied concentrations produces β-factors that are constant within ∼0.02‰. Finally, we discuss the implications of our results for the interpretation of recent experiments and the understanding of core crystallisation processes.

铁是太阳系中最丰富的非挥发性元素之一。作为行星金属合金的主要成分，它与硅酸盐的不混溶性在行星的形成和分化中起着重要作用。通过研究在岩心形成条件下金属合金和熔融硅酸盐之间的平衡铁同位素分馏，可以获得有关这些过程的信息。尤其是最近关注⁵⁶ Fe/ ⁵⁴Fe 平衡同位素分馏在与地球核心形成相关的条件下以及轻元素（O、H、C、Ni、Si 和 S）在此过程中的影响。大多数这些实验研究依赖于对来自硅酸盐熔体和铁水合金淬火相的 Fe 同位素分馏的测量。实验工作极具挑战性，可能会遇到不同的缺点。为了克服这个问题，我们使用ab-initio计算方法对熔融和固体 Fe _{1− x} S _x中的⁵⁶ Fe/ ⁵⁴ Fe 平衡同位素分馏进行系统研究合金在核心形成条件下 (60 GPa, 3000 K)。我们首次表明，在相关PT条件下，这两种方法之间的差异小于 0.01‰，可以将来自固体系统的平衡同位素分馏因子用作熔融系统的代理。此外，我们讨论了硫浓度对平衡 Fe 同位素分馏的影响，并表明虽然由于原子取代存在一些结构变化，但广泛的研究浓度产生了β因子，这些因子在 ~0.02‰ 内是恒定的。最后，我们讨论了我们的结果对解释最近的实验和理解核心结晶过程的影响。