Thermoelastic properties of minerals and melts are the crucial link that permit seismic tomography images of the Earth's interior to be translated into information of geophysical significance: mineralogy, composition, and temperature. Over the last decade, enormous advances have been made in our ability to compute elastic properties of materials under the extreme conditions of Earth's interior using only the fundamental constants of nature as input. Nevertheless, great challenges remain, especially regarding iron bearing minerals. In oxides and silicates, iron has magnetic moment and its electrons are strongly correlated. Materials with strongly correlated electrons have challenged theorists for more than half century and mantle minerals are among the most complex of them. Besides, their behavior must be understood at extreme conditions of pressures and temperatures, which change their magnetic state, a phenomenon known as spin transition. Under this grant novel methods based on the DFT+U approach will be applied to investigate spin transitions and its consequences for the thermoelastic properties of the most important phases of Earth's lower mantle: ferropericlase, ferromagnesium silicate perovskite and postperovskite. Fe2O3 is a possible stable phase at the core-mantle boundary and an ideal material for testing the new methods. Atomic vibrations, atomic diffusion, and collective magnetic excitations will be studied to shed light on the thermal, elastic, rheological, and transport properties of these phases and of the mantle.
The outcome of this research will be essential input for researchers investigating the state and evolution of the mantle. The novel methods, whose development is being stimulated especially by mineral physics, have been implemented in the open source at initio materials simulation package Quantum ESPRESSO. They will be available in subsequent releases of the package to the mineral physics and materials communities. The PIs are deeply involved with education and outreach programs that include a) training of graduate students and post-docs, b) training of undergraduates through summer internships offered through the Minnesota Supercomputing Institute, and c) giving tutorials to the materials and mineral physics community.
