[sdpd] Transforming predictions into solution

[Armel Le Bail <alb...@cristal.org>]

Hi,

Comments on two interesting papers in the latest
J. Appl. Cryst. issue 6 (2005).

Both papers are about transforming crystal structure
predictions into solution, through powder data.

The first paper entitled "New similarity index for
crystal structure determination from X-ray powder
diagrams" (J. Appl. Cryst. 38, 2005, 861-866)
proposes a method to compare efficiently observed data
to a series of calculated patterns from structure predictions
(the first 100 high-ranking predicted models, ranked by energy,
obtained by packing considerations, searched
in the 11 most common space groups, covering 82.7%
of all structures collected in the CSD). Applications
are made to solving the structures of pigments.
The method is tolerant to large deviations in cell
constants (leading to observed and calculated peak
position discrepancies).


The second paper, entitled "A systematic topological
search for the framework of ZSM-10" (J. Appl. Cryst.
38, 2005, 1028-1030) uses the exhaustive enumeration
of every possible topology consistent with known uni-cell
dimensions and space group symmetry. Presently, the
database contains over a million zeolite frameworks, and
continues to grow.

The contrast between the two papers is there : 1.000.000
models for zeolites (but less than 200 structures known), for
the simple SiO2  formulation, and 100 models only for a given
pigment ensuring good chances of success. Another
difference there is that limiting oneself to only 11 space
groups would not ensure a lost of chances of success for
inorganic compounds...

As a conclusion, until the crystal structure prediction of a
material in arbitrary themodynamic conditions is not totally
efficient, we cannot pretend to have established
a successful theory of materials... Reducing the number
of models to the most likely ones would allow the
production of a PPDF (Predicted Powder Diffraction
File).

Plug in you brain on that question...;-).

Armel

PS - A new series of GRINSP-predicted titanosilicates will
soon appear into the PCOD (Predicted Crystallography
Open Database : http://www.crystallography.net/pcod/)



------------------------ Yahoo! Groups Sponsor --------------------~--> 
Get fast access to your favorite Yahoo! Groups. Make Yahoo! your home page
http://us.click.yahoo.com/dpRU5A/wUILAA/yQLSAA/UIYolB/TM
--------------------------------------------------------------------~-> 

 
Yahoo! Groups Links

<*> To visit your group on the web, go to:
    http://groups.yahoo.com/group/sdpd/

<*> To unsubscribe from this group, send an email to:
    sdpd-unsubscribe...@yahoogroups.com

<*> Your use of Yahoo! Groups is subject to:
    http://docs.yahoo.com/info/terms/