Prsentation PowerPoint

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The third Structure Determination by Powder
Diffractometry Round Robin (SDPDRR-3) L.M.D.
Cranswick and A. Le Bail Canadian Neutron Beam
Centre, National Research Council Canada,
Building 459, Chalk River Laboratories, Chalk
River ON, Canada, K0J 1J0. Email
lachlan.cranswick_at_nrc.gc.ca Université du Maine,
Laboratoire des Oxydes et Fluorures, CNRS UMR
6010, Av. O. Messiaen, 72085 Le Mans, France.
Email Armel.Le_Bail_at_univ-lemans.fr
INTRODUCTION The results from a third structure
determination by powder diffractometry (SDPD)
round-robin are summarized. From the 175
potential participants having downloaded the
powder data, 9 have sent a total of 12 solutions
(8 and 4 respectively for samples 1 and 2, a
calcium tartrate tetrahydrated and a lanthanum
tungstate). They used 7 different computer
programs for structure solution (ESPOIR, EXPO,
FOX, PSSP, SHELXS, SUPERFLIP, TOPAS),applying
either the Patterson or direct methods, direct
space methods, or the charge flipping approach.

Sample 1 CaC4H4O6.4H2O
Conventional X-rays

Sample 2 La18W10O57
Synchrotron
Neutron
CONCLUSION Solving a structure from powder data
remains a hard job, an order of magnitude harder
than solving a problem with similar complexity
from single crystal data. Nevertheless, a few
more steps in the direction of routine were
accomplished since the two previous round-robins
that time, not only the computer program
developers were successful, but also some more
standard users. No result was obtained from
crystal structure prediction experts.

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