  In this work, we demonstrate a remarkable change of chemical trend of Iron
under high pressure that is of great importance for understanding the
distribution of elements in the Earth's mantle and core. Using first principles
crystal structure search method, we conduct a systematic study of the
propensity of p block elements to chemically bind with iron under high
pressures ranging from ambient conditions to that of Earth's core. We show that
under increasing pressure, iron tends to reverse its chemical nature, changing
from an electron donor (reductant) to an electron acceptor, and oxidizes
p-block elements in many compounds. Such reverse chemistry has a significant
impact on the stoichiometries, bond types and strengths, structures and
properties of iron compounds under deep planetary conditions.
