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Quantification of complex disordered phases by a parallelized Rietveld program

Joerg Bergmann 1,  Kristian Ufer 2,  Reinhard Kleeberg 2

1. Private, Ludwig-Renn-Allee 14, Dresden 01217, Germany
2. Freiberg University of Mining and Technology, Mineralogical Institute, Brennhausgasse 14, Freiberg 09596, Germany

Abstract
The correct modeling of diffraction patterns of disordered layered structures within the Rietveld method is a need for more accurate quantitative phase analysis (QPA) e.g. of clay-bearing rocks. Different approaches have been developed to approximate the diffraction profiles of distorted layered structures. Simple anisotropic (hkl dependent) line broadening models based on small ideal unit cells are often not sufficient to describe the real disorder features. Alternative approaches like the one-dimensional elongation of cells in the "single layer approach" (Ufer et al., 2004), combined with the recursive description of layered structures (Treacy et al., 1991) result in the generation of a large number of atomic positions respective a high number of diffraction peaks. This leads to an immense computational effort.

Especially the recursive calculation method requires large quantities of computing power. Nowadays, multi-core CPUs become more accessible and widely used in modern PCs. So it suggested itself speeding up these calculations by parallelizing the Rietveld code. Consequently, the used Rietveld program BGMN was multithread-enabled.

As a principle of development, the BGMN system remains highly portable. Wrapper functions were written for the basic multithreading operations. Therefore, the parallelized BGMN remains usable under Windows as well as under Linux. The principles of parallelization will be described in brief.

The capability of the enhanced computation procedure will be demonstrated on multiple examples. Benefits and features of this Rietveld code will be discussed. The speedup of computation on different hardware/operating systems, for simple mixtures as well as for samples containing multiple disordered phases, will be shown. In practice, a phase quantification of mixtures containing up to 14 minerals including 4 heavily disordered clay minerals was possible with satisfying results within 30 min on a dual Quad Core computer.

[1] K. Ufer, G. Roth, R. Kleeberg, H. Stanjek, R. Dohrmann, J. Bergmann,
Description of X-ray powder pattern of turbostratically disordered layer
structures with a Rietveld compatible approach.
Z. Kristallogr. 219 (2004) pp. 519-527

[2] M. M. J. Treacy, J. M. Newsam, M. W. Deem,
A general recursion method for calculating diffracted intensities from
crystals containing planar faults.
Proc. R. Soc. London A433 (1991) 499-520

 

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Related papers
  1. State-of-the-art and trends in quantitative phase analysis of geological and raw materials

Presentation: Poster at 11th European Powder Diffraction Conference, Poster session, by Joerg Bergmann
See On-line Journal of 11th European Powder Diffraction Conference

Submitted: 2008-04-26 17:53
Revised:   2009-06-07 00:48