Collaborative Research: Thermodynamics and thermoelasticity of iron-bearing phases

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The deep mantle of Earth and other solar terrestrial planets consists of iron-bearing minerals. Earth-type planets orbiting other stars (terrestrial exoplanets), including the large super-Earths, must contain iron-bearing phases as well. These phases are subjected to the extreme pressures and temperatures prevailing in deep planetary interiors. Investigating their thermodynamic and thermoelastic properties is a fundamental step toward understanding the processes responsible for planet formation and evolution. It is also important when investigating planet internal structure and dynamics. Here, the researchers explore the structure and properties of mantle iron-bearing phases at extreme conditions. They carry out systematic calculations at the atomic scale, called ab initio because they address electrons quantum mechanically. They use innovative methods to quantify the electronic state of iron, a key player which greatly impacts materials properties. The team also performs numerical simulations of planet dynamics to constrain mantle evolution and present-day structures. The project's outcomes have strong implications for the understanding of Earth's mantle dynamics, notably its thermal convection which constrains plate tectonics and associated hazards. The new simulation methods, shared with the community, can be applied to other materials. This multidisciplinary project - at the crossroad of materials science, mineral physics, and geodynamics - provides support for postdoctoral associates and graduate students. It also fosters educational outreach toward undergraduate students and the public. Here, the team tackles a fundamental class of problems in high-pressure mineral physics by bringing together experts in the physics of strongly correlated electrons and Earth forming phases. Iron-bearing oxides and silicates contain strongly correlated electrons which are challenging for ab initio calculations. This is particularly true at pressures in the TPa range (tens of millions of atm) and temperatures in the 10,000 K range (tens of thousands of degrees Fahrenheit). The researchers develop new codes to address this challenging problem and attendant effects, such as spin transitions. They use state-of-the-art methods such as self-consistent density functional theory plus Hubbard U (DFT+Usc) and an adaptative generic algorithm (AGA). New codes will be release as stand-alone software or in subsequent releases of the Quantum ESPRESSO software. This popular open source software for ab initio materials simulations has a broad community of users across disciplines. Results generated in the course of this research are made available through a public database and interactive websites. The team also fosters educational outreach toward undergraduate students and the public, and international collaboration with the Netherlands and Canada.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.