Ab- initio Molecular Dynamics for EXAFS Analysis of Trace Impurities in Geochemistry (Micah Prange) скачать в хорошем качестве

Ab- initio Molecular Dynamics for EXAFS Analysis of Trace Impurities in Geochemistry (Micah Prange)

Title: Ab- initio Molecular Dynamics for EXAFS Analysis of Trace Impurities in Geochemistry Speaker: Dr. Micah Prange (PNNL) Understanding and controlling the incorporation of trace metal impurities in earth abundant solid host phases is a marquee challenge for geochemistry, with applications concerned with sequestering undesirable species, separating desired ones, or tuning the properties of the host. In all cases, the thermodynamics and energetics of the incorporation reactions are determined by the local structure of the impurity element. The elemental specificity of EXAFS analysis makes it an indispensable tool to probe such coordination environments, but its application is complicated in the case of impurities relative to pure phases by the configurational disorder (variety) of incorporation motifs. Thermal and configurational disorder are often difficult to disentangle in conventional EXAFS fitting methods. Faithful simulations of equilibrium thermal motion using ab initio molecular dynamics can improve the situation. In this talk, I will describe methods and viewpoints developed by the geochemistry group at Pacific Northwest National Laboratory over the last decade that use ab initio molecular dynamics simulations as virtual samples that yield theoretical standards to fit impurity EXAFS spectra as well as other experimental data, like X-ray total scattering (PDF). I will highlight work on iron ((oxy)hydr)oxide and carbonate solids that demonstrates that these methods can be used to understand crystalline and amorphous host materials. I will end with a brief and speculative discussion on the information content of complementary experimental modalities and the prospects for combined interpretations of multimodal data sets using atomistic dynamics simulations.