Naslov
Improving the Accuracy of Structures Solved by Powder Diffraction

Autori
Halasz, Ivan ; Dinnebier, Robert

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
12th European Powder Diffraction Conference / - , 2010

Skup
12th European Powder Diffraction Conference

Mjesto i datum
Darmstadt, Njemačka, 27.08.2010. - 30.08.2010

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
powder diffractiom ; accuracy ; simulated annealing ; Rietveld refinement

Sažetak
Crystal structure models used as starting models for Rietveld refinement, may not be close enough to the global minimum to allow for convergence. More likely, the refinement will be trapped in a nearby local minimum. We suspect that this is often the case with moderately sized crystal structures of molecular compounds, thus hindering precise structure determination. Herein we describe how performing a series of optimizations from slightly different starting models may help finding the global minimum (model which gives the best fit to the measured data). The program Topas [Version 4.1, Bruker-AXS, Karlsruhe, Germany] allows the user to define new starting values of parameters (by e.g. adding a random small shift) before a new refinement cycle is initiated. Since molecular geometry is distorted after the shifts are applied, setting the proper values of geometry restraints seems to be crucial. By applying this method the system explores the space around the initial model which allows for the determination of the global minimum with better reliability (Fig. 1). We will present refinements on two moderately sized compounds, for both of which lower minima were found after this approach was applied.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

POVEZANOST RADA