Séminaire - Extracting local structure information from X-ray spectra on amorphous materials under pressure - Keith Gilmore

Jeudi 11 avril 2019 à 14 h

IMPMC - Sorbonne Université - 4 place Jussieu, 75005 Paris, tour 23, 4^e étage, couloir 22-23, salle 401

Keith Gilmore - Brookhaven National Laboratory, New York, USA

Abstract

In many cases, systems under pressure may be amorphous, which significantly complicates structural characterization as a function of pressure.  With the absence of long-range order, one seeks to make statements about an ensemble of local coordinations.  Core-level spectroscopy, which is sensitive to local electronic and atomic structure, and element specific, yields information on local coordination.  However, one observes only an averaged signal, which is typically featureless and difficult to interpret.  We have found success in a trinity of experimental spectroscopic measurement, molecular dynamics simulation, and spectroscopic calculation [1].  This approach is suitable for X-ray absorption, X-ray emission, and non-resonant inelastic X-ray scattering spectra, and we have applied it to pressurized silica [2], GeO2 [3] and liquid water [4].  This talk introduces the computational methodology for calculating the relevant X-ray spectra [5] as well as a procedure for extracting detailed information from spectra taken on amorphous materials under high pressure.