Electron transfer is the most elementary process in nature, but the existing electron transfer rules are seldom applied to high-pressure situations, such as in the deep Earth. Here we show a deep learning model to obtain the electronegativity of 96 elements under arbitrary pressure, and a regressed unified formula to quantify its relationship with pressure and electronic configuration. The relative work function of minerals is further predicted by electronegativity, presenting a decreasing trend with pressure because of pressure-induced electron delocalization. Using the work function as the case study of electronegativity, it reveals that the driving force behind directional electron transfer results from the enlarged work function difference between compounds with pressure. This well explains the deep high-conductivity anomalies, and helps discover the redox reactivity between widespread Fe(II)-bearing minerals and water during ongoing subduction. Our results give an insight into the fundamental physicochemical properties of elements and their compounds under pressure.

Extensive AO 2 -type transition metal (TM) oxides are experimentally determined or theoretically predicted to adopt the pyrite-type (Pa3̅ ) structure at different pressures, but their physical and chemical properties are largely unknown. Our theoretical calculations demonstrate that the interpolyhedral O−O bond is formed in pyrite-type CoO 2 with low-spin Co 2+ similar to the case of FeO 2 , whereas ferromagnetic CrO 2 and antiferromagnetic MnO 2 belong to dioxides with separate O 2− anions. The oxidation state of the cation and the potential formation of O−O bonding are affected by the crystal-field splitting, charge transfer between the cation and the anion, but primarily by the magnetic coupling among 3d electrons in a pyrite-type 3d TMO 2 . The spin crossover-induced magnetism-vanishing at high pressures contributes to a smaller cell volume and a weaker electronic correlation, facilitating the formation of an O−O bond and a reduction of the oxidation state of the cation. These results provide critical physical insights into the formation mechanism of 3d TM peroxides with O 2 2− dimers. Based on this conclusion, we have further theoretically predicted the formation of the hydrogen-bearing cobalt peroxide at high pressures. This shows another example for exploring the nature of hydrogen-bearing TM peroxides and sheds light on synthesizing novel TM peroxide materials under high pressure.

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