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Software
GSAS_USE (Bayesian Statistics Approach to Accounting for Unknown Systematic Errors)
GSAS_USE addresses the effects of systematic errors in Rietveld refinements. The errors are categorized into multiplicative, additive, and peak-shape types. Corrections for these errors are incorporated into using a Bayesian statistics approach, with the corrections themselves treated as nuisance parameters and marginalized out of the analysis. Structural parameters refined using the proposed method represent probability-weighted averages over all possible error corrections.
BBEST Bayesian Estimation of Incoherent Neutron Scattering Backgrounds
We implemented a Bayesian-statistics approach for subtraction of incoherent scattering from neutron total-scattering data. In this approach, the estimated background signal associated with incoherent scattering maximizes the posterior probability, which combines the likelihood of this signal in reciprocal and real spaces with the prior that favors smooth lines.
NANOP
This software package simulates spherical, ellipsoid and cubic polyatomic nanoparticles with arbitrary crystal structures and calculates the associated pair-distribution function and X-ray/neutron total-scattering signals. It provides a target function used for simultaneous fitting of small- and wide-angle total scattering data in real and reciprocal spaces. The target function is generated either as a sum of weighted residuals for individual datasets or as a vector of residuals suitable for optimization using multi-criteria algorithms (e.g. Pareto methods).
RMCProfile
RMCProfile is a free software package (developed as a collaborative effort between scientists at several institutions including NIST), that can fit simultaneously different types of diffraction and spectroscopy data using a Reverse Monte Carlo (RMC) algorithm to determine both local and average atomic arrangements in a broad range of materials. The NIST team focuses on the development of multi-technique aspects of this analysis and on the optimization of the software’s computing speed to enable handling of larger atomic configurations.
RMCProfile Utility Programs
RMCProfile is a free software that can fit simultaneously atomic pair-distribution function, total scattering function S(Q), and Bragg profile under various geometric and bond valence sum constraints. Developed at NIST, an extension to RMCProfile enables a simultaneous fit of neutron/X-ray total scattering data, Extended Absorption Fine Structure (EXAFS) (real space), and a geometric shape of diffuse scattering in electron/X-ray single-crystal diffraction.
gppois
gppois is a Bayesian tool for learning about a smooth function based on noisy measurements of its values. Users train a model of the true function on the noisy datapoints, then use that model to make predictions at whatever points they desire to know.