This dataset contains VASP runs performed on several supercomputing services (Monsoon and ARCHER, and their successors Monsoon2 and ARCHER2) to calculate the chemical potentials of potassium in liquid iron mixtures and in liquid and solid silicate mixtures, and their distribution in the Earth’s core using density functional theory. Data are available for the chemical potentials of potassium and various other elements in iron and silicate liquid mixtures. These data were used to calculate chemical equilibrium between liquid iron alloys and Earth’s mantle materials. The present grant also supported work regarding the Si composition and thermal history of Earth’s liquid core. Results from VASP runs are also included in the uploaded dataset.