Application of the embedded-atom method to liquid Fe-S solutions

A procedure (proposed earlier to describe liquid Fe) for calculating the embedded-atom method (EAM) potential with the use of structural and thermodynamic data for the metal near its melting point has been applied to liquid Fe-S solutions at temperatures of up to 5000 K and pressures of up to 360 GPa. Molecular dynamics simulations have been carried out for solutions with 0-18 at % S with the EAM potential at temperatures from 1820 to 5000 K and densities from 10.69 to 12.28 g/cm(3). We have calculated the thermodynamic, structural, and diffusion properties and estimated the viscosity of noncrystalline phases. At a pressure near 360 GPa and a temperature of 5000 K, pure iron crystallizes spontaneously, while the solutions of sulfur in iron behave as high-viscosity liquids or amorphous phases with a self-diffusion coefficient on the order of 10(-7) cm(2)/s and a viscosity of up to tens of Pa s. As the sulfur content increases from 0 to 6.2 at %, the viscosity first decreases and then rises. During long-term relaxation, the model of an Fe-S solution may turn into a crystalline-like state. The origin of marked discrepancies between ab initio and EAM simulation results is discussed.