Quantum Mechanics Explains Solubility Of Hydrogen In Earth's Iron Core

Detailed knowledge of the structure, dynamics, and chemical composition of the earth’s crust is important to modern geo-scientific research about the development of the earth and ongoing changes. The earth’s solid inner core, from 2,900 km inward to the middle of the earth, consists primarily of iron, but lighter elements such as sulfur, carbon, silicon, and hydrogen could possibly be included. However, the exact consistency is not known.

In 1980, using high pressure, researchers managed for the first time to produce an compound of iron and hydrogen, iron hydride. This was a surprise, since this compound does not occur under natural conditions. In other words, it is fully possible that hydrogen exists in the iron core of the earth. But geophysical or mineral chemical data are hard to achieve using experimental methods only, since the pressure and temperature in the core of the earth are so extreme. Theoretical models can therefore provide key knowledge.

In the present study, researchers used calculations in quantum mechanics to discover that the properties of iron hydride change with pressure, finding that they can explain current discrepancies between experimental and theoretical data. By factoring in the vibrations of atoms and how these vibrations change with pressure, they were able to eliminate the troublesome deviations. These calculations can also be used for predicting transfer properties such as the conduction of heat in the earth’s core.

“For the first time this study presents the principles for the stability of iron together with hydrogen under pressure conditions relevant to the inner parts of the earth,” says Börje Johansson, professor of the theory of condensed matter at Uppsala University and the Royal Institute of Technology in Stockholm.

The extensive numerical studies were performed at Uppsala University’s Uppsala Multidisciplinary Center for Advanced Computational Science, UPPMAX.