Formation of Stable Compounds of Potassium and Iron under Pressure.

We predict stable stoichiometric potassium-iron (K-Fe) intermetallic compounds at high pressures from first principles. Thermodynamic stability, crystal structures, and bonding properties of these compounds are also investigated. The dynamic stability of the predicted structures is established through phonon calculations while mechanical stability is established through Born-Huang stability criteria. Our results reveal that potassium and iron can form intermetallic compounds that are stabilized by high pressure and energy reordering of atomic orbital through electron transfer. A K-rich K-Fe compound is predicted to undergo structural phase transformations under pressure where clustering of K atoms is observed to precede transformation into the Fe-rich phase above 120 GPa. The elastic velocities and the densities predicted for various K-Fe compounds suggest that they may explain a potassium-containing Earth's core.