SPEC Summary

Main theoretical research reference:

Theoretical and computational methods in mineral physics: geophysical applications.

Vol. 71. Mineralogical Society of America, 2010.

Wentzcovitch, Renata and Stixrude, Lars

http://static.msi.umn.edu/rreports/2010/25.pdf (current unavailable)

Summary

The principal investigator’s (PI) contribution to this field has been seminal. In particular, she developed computational methods that opened to way to first principles calculations in mineral physics. She introduced techniques for calculations of thermodynamics and thermal-elastic properties of materials in general. These properties are of first order importance in geophysics and planetary modeling. Thermal-elastic properties are fundamental for calculations of acoustic velocities in crystalline and poly-crystalline materials (rocks). These are being successfully used to interpret seismic tomography data.

Thermodynamics properties - more specifically thermal expansion coefficient, specific heat, compressibility, and thermodynamics phase boundaries - are being used to improve the realism of geodynamics simulations. These detailed calculations of mineral properties are enabling modeling of Earth and other planets from the atomic to the global scale. It is allowing for direct integration of these three branches of geophysics, i.e., seismology, geodynamics, and mineral physics. Novel methods to compute electrical conductivity, dielectric, magnetic, and optical properties in bulk materials also promise to make an impact in geodynamo modeling and paleo-magnetism. This integration, described in details in the proposal, provides the foundation and long term vision for an original research program in Brasil and hopefully in the world, a “Virtual Earth Institute”. The proposed research aims to initiate this project and will focus on computational mineral physics.

Proposed problems

Here we describe three classes of Earth and planetary science problems to be addressed by this research program. High throughput first principles calculations are essential to advance them. Extensive results will be generated and made available online using new technology proposed in the next section.

1. Mantle structure, composition, and temperature

Advances in seismic imaging of the Earth's deep interior are providing structural information about convective and thermal patterns in the lower mantle. Several fascinating structures holding keys to the nature of the deep mantle are currently being seismologically mapped in detail. These require self-consistent interpretations compatible with mineralogically and geodynamically feasible contexts. Examples are: i) two nearly antipodal large low-shear-velocity provinces (LLSVPs) with abrupt lateral boundaries in the deep mantle, which likely represent chemically distinct and denser material whose nature is still unclear; ii) isolated pockets (zones) of ultra-low seismic velocities (ULVZs) in the deepest tens of kilometers of the mantle, may indicate the presence of deep magma chambers or accumulations of materials highly enriched in iron; iii) the long-standing problem of mantle composition, inseparable from large scale convection patterns in the Earth. This problem needs to be re-investigated in light of novel results on the Fe spin-state crossover in lower mantle minerals [43-45,56]. It has recently become clear that their manifestation might be interpreted as chemical heterogeneity [56].

2. H2O in the mantle

Three broad themes in which H2O ¬ plays a critical role in geophysics are: i) cycling of water through the Earth’s deep interior [261-264] (see Fig. 13), ii) the influence of water on melting and other phase transitions in the deep mantle [265,266], and iii) seismic detection of water in the mantle [277], which would be very helpful to advance understanding of i) and is intimately related with ii). In recent years there has been a tremendous effort by the deep Earth community to determine the influence of H2O on mantle properties, but key questions remain unanswered. We still do not have strong constraints on the inventory of H2O in different layers of the Earth, nor do we know the fluxes of H2O between these layers or the locus of melting induced by H2O in the deep mantle. We have made significant progress toward understanding the microscopic role played by trace substitutions of H in nominally anhydrous minerals (NAMs) [268], particularly on the effect of hydration on phase transitions in MORB at mantle pressures [269]. Such microscopic effects must be pervasive in mantle minerals.

3. Exoplanetary materials

This research concerns a novel challenging area of computational materials theory: properties of matter at extreme conditions of pressure (P) and temperature (T), i.e., T ~ 3 eV, P ~ 10 TPa, and beyond. This research is fundamental for advancing understanding of the internal structure of giant planets [111] and exoplanets [99,100], particularly of the terrestrial type [101]. This is clearly an area that presents remarkable opportunities for interdisciplinary discoveries of high scientific impact and methodological developments broadly applicable to other areas of materials discovery. Controlled experiments at these conditions are virtually impossible. However, it is possible to connect this research with experimental data by investigating low pressure analogs.

Introduction

Geophysics stands on a synergistic tripod consisting of seismology, geodynamics, and mineral physics and advances by close cooperation between these fields that can be computationally very intensive.

Mineral physics’ role is to provide information on mineral properties that are needed i) to interpret seismic tomography and ii) to bolster advanced and more refined geodynamics simulations. Computational mineral physics has contributed greatly to the integration of these fields by complementing experiments by expanding the pressure (P) and temperature (T) range in which properties can be obtained. With the discovery of extra-solar planets, particularly of the terrestrial type, its role has expanded in range of physical conditions, type of materials, and materials properties to be investigated. Today mineral physics interfaces also with planetary sciences. For many problems, first principles computations based on density functional theory (DFT) [1,2] and its successful implementations and extensions [3-8] is the most or only practical method of investigation. This capability has been changing the scientific landscape in Earth and planetary sciences. Successes and contributions of computational mineral physics are already too numerous to cite. They cover thermodynamics properties and phase boundaries, discovery of new phases relevant for Earth and exoplanets, and thermal elastic and transport properties of minerals and melts. A snapshot of this evolving field was captured in a special volume published in 2010 [9]. Since then progress has accelerated as will be demonstrated in this proposal. These contributions have been possible by a combination of methodology and algorithmic innovations, availability of reliable commercial [10-13] or free open source [14,15] first principles codes, and steady increase in computational power. We have now entered another transformative stage in computational mineral physics. Cyberinfrastructure (CI) [16] is enabling a leap in computational capability. It is helping to produce huge amounts of results tens of times faster than were produced five years ago and to communicate them thoroughly and in detail online.

The main goals of this proposal are:

1) to strengthen the synergy between computational mineral physics, seismology, geodynamics, and planetary sciences. PI, co-PIs, and collaborators bring to this project a rich history of breakthroughs, accomplishments, and synergies. Some of the PI’s Previous accomplishments reviewed in the next section illustrate technological possibilities and recent scientific advances. We wish to continue using and developing them in the context of projects outlined in the Proposed problems section tapping local expertise in materials theory and simulations and Earth and planetary sciences. The Departamento de Física dos Materiais e Mecânica from Instituto de Física, USP, has a long tradition of research in first principles calculations. Prof. Luiz Guimareães Ferreira, a pioneer in this field, Profs. Lucy C. Assali and Helena Petrilli, with their extensive research experience in semiconductor physics, solid solutions, polymers, and defects in solids and in using/developing first principles calculations are co-investigators in this project. Prof. João Francisco Justo, from the Polytechnic School, is another co-investigator. He has collaborated with the PI in mineral physics and is the scientist in São Paulo that most closely relates to the PI’s research. They will be instrumental in building a bridge to the local seismology, geodynamics, geochemistry, and planetary sciences communities, here represented by Prof. Ricardo Trindade, a geochemist, Dr. Victor Sacek, a geodynamicist, and Dr. Marcelo Bianchi, a seismologist from Instituto Astronômico e Geofísico (IAG), USP. They provide the motivation for our research are are the “consumers” of our results, since they will make direct use of our “data” in their modeling;

2) to enable cyber-infrastructure applications in this field. Planetary interior modeling requires detailed information on mineral properties in a continuum of pressure-temperature-composition-phase fields. This is essentially impossible to report in written form or to calculate using standard technology for materials simulations. These are high throughput calculations and we have developed a special cyber-infrastructure consisting of a portal, web services, and databases to obtain and report these properties – the VLab CI [16-22]. It is essential for Earth and planetary sciences applications requiring mineral physics data and we want to have it locally supported. Prof. Sérgio Ferraz Novaes, from the Institute of Theoretical Physics Institute (IFT), UNESP, will host the VLab cyber-infrastructure in his data center. He has….;

3) training of exchange students and post-docs and developing the future generation of scientists working in these related field. Organization of workshops, conferences, and tutorial courses in São Paulo will also connect scientists in São Paulo to new communities abroad and will hopefully activate other collaborations as well. PI and co-PIs have extensive experience with organization of such events.

-- winckler - 2015-09-11