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Theory of Mantle, Core and Technological Materials

Final Report Summary - TOMCAT (Theory of Mantle, Core and Technological Materials)

We have used fundamental physics on supercomputers to predict properties of Earth and technological materials. Using computational quantum mechanics, and no essential input other than the atom types, we have studied a wide variety of materials, made predictions important for Earth and Planetary science, designed new materials which may be useful to society, and generally improved our understanding and ability to further understand nature. We have made a number of important discoveries in several fields. We have predicted the electrical and thermal conductivity of iron in Earth's core, and find that classic dynamo theories, that describe the generation of Earth's magnetic field, can be driven by thermal convection, in contrast to recent claims to the contrary. We have generated results that will better describe giant planet interiors, like Jupiter, and constrained properties of aqueous fluids in the Earth. We have designed new active materials that can interchange different types of energy, and studied how they can extract energy from waste heat or cool solid state devices.
Our main tool for this project was first-principles molecular dynamics. One solves for the energy and forces of an atomic system using density functional theory (DFT). DFT is a formally exact theory that is approximate in practice, but is still requires a lot of computing power. We find the forces F on the atoms, and then move them according to Newton's law, F = m a, where m is the atomic mass and a the atomic acceleration for each atom. The faster the atoms move, the higher the temperature, and the closer they are together the higher the pressure. Using this approach we have studied supercritical water-CO2 at conditions of the Earth where subducted slabs lose their fluids by being heated in the Earth's interior, and fluid iron-hydrogen at condition up to the center of Jupiter and beyond (over 10-50 million atmospheres of pressure and temperatures up to 40,000 K. These are huge computa tions that require fast supercomputers. We gratefully acknowledge the Gauss Centre for Supercom puting e.V. (www.gauss-centre.eu) for providing computing time on the GCS Supercomputer Super MUC-NG at Leibniz Supercomputing Centre (www.lrz.de).
A major effort went into understand the electrical and thermal conductivity of iron in Earth's core. This is a key parameter that governs Earth's thermal history and the generation of Earth's magnetic field. We used several different methods to cross check our work, because this has become a very controversial area since it was proposed that iron was too conductive to convect and generate Earth's magnetic field through classic dynamo theory. We found that the conductivity is not too high to have thermal convection, and also obtained good agreement with next high pressure experiments.
We also studied the most common mineral in the Earth, silicate perovskite, to obtain accurate predictions of its properties at the high pressure conditions in the deep Earth. In the lower pressure regime, we studied filled ices, which we predict are important in Saturn's largest moon Titan, and similar moon and exoplanets.
As well as studying Earth and planetary materials, we used the same methods to study active materials such as ferroelectrics. We studied the effects of small amounts of dopants (impurities) and how they can improve ferroelectric properties by up to a factor of 3 or better, by general small electric fields inside the material. We studied also how these impurities affect the magnetic properties, and how they can form ferromagnetism, which leads to an important effect called multiferroism, where magnetic and electric effects are both coupled with shape changes in a material. We also simulated the electroccaoloric effect, where the temperature of a material changes with an applied electric field. This can lead to new energy efficient refrigeration as well as extracting energy from waste heat.
This is a sample of results of this wide-ranging project on materials important in the Earth and planets and for technology.