Re: How much COD and PDF database gives the complete known structures?

[xtal]

At 17:12 10/01/2017 +0200, Shay Tirosh wrote:

Dear retrievers

I wander the followings:
1. How much COD and PDF overlaps?


Indeed the answer is funny.

It depends on you.
How much of your own data have you sent to COD ?
If zero, then there is no overlap at all, your own data will
be only in PDF (unless you published in journals allowing
the COD to grab for data, but they are very few).


2. What I am missing if I only search in COD and PDF?


Same funny answer, given that the number of crystallographers
sending their own data to the COD is itself absolutely funny.

Best,

Armel Le Bail

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Re: 3D whole pattern fits for SFX data

[xtal]

At 14:23 02/03/2016 +0100, Jonathan WRIGHT wrote:

3D whole pattern fitting has arrived:

http://dx.doi.org/10.1107/S2052252516001238

... and the samples are powders!


Not Pawley (up to now)...

Armel


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Re: CIF of CH3NH3PbI3

[xtal]

Dear Shay,

Could be that one with a = b ~ c ~ 6.31 A ?
http://www.crystallography.net/4335634.html?cif=4335634
And there is another polymorph :
http://www.crystallography.net/4335634.html?cif=4335638
Both in a recent 2013 paper :
Title of publication : Semiconducting Tin and Lead Iodide Perovskites with 
Organic Cations: Phase Transitions, High Mobilities, and Near-Infrared

Photoluminescent Properties
Authors of publication : Constantinos C. Stoumpos; Christos D. Malliakas;
Mercouri G. Kanatzidis
Journal of publication : Inorganic Chemistry
Year of publication : 2013
Journal volume : 52
Pages of publication : 9019 - 9038

Best,
Armel

At 18:18 06/12/2014 +0200, Shay Tirosh wrote:

Dear Reitveldrs

In case someone have, can you please send me the CIF of the cubic Pm3m
phase CH3NH3PbI3.
I was unable to find it on the web.

Thank you from advance

Shay



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Re: [sdpd] Re: Are restraints as good as observations ?

[xtal]

At 03:04 02/08/2013 -0700, Leonid Solovyov wrote:

remember the previous discussion at the
Rietveld list where he claimed that all H
can be seen and refined independently, always.

Absurd - never said so.
From absurdity and crimes we arrived at falsifications?


Below are the unfalsified words.

Ugly yours, with pestilence,

Armel

PS- rigid brain is the first step before rigid body

=
Subject: DDM program update 1.92
Date: Sun, 16 Oct 2011 20:41:12 -0700 (PDT)
From: Leonid Solovyov l_solov...@yahoo.com
To: rietveld_l@ill.fr

Dear Colleagues,

The DDM program update 1.92 with some minor bugs fixed is available at
http://sites.google.com/site/ddmsuite/
and
http://l-solovyov.narod.ru/ddm.html

The folder EXAMPLES\H-atoms\ now contains 15 instances of unconstrained 
refinement of H-atoms from XRPD data of various quality and complexity.


A good illustration to the recent SDPD discussion on H-atoms and restraints 
is the structure of C7H6ClN3O4S2 that was refined previously by a 
restrained Rietveld using a combination of XRD and neutron data [Acta 
Cryst. B (2008) 101]. By DDM it is refined from XRD data solely without 
restraints including 6 independent H-atoms 
[EXAMPLES\H-atoms\C7H6ClN3O4S2.ddm]. In the alternations of C-C and C-N 
distances and angles the alternations of singe and double bonds is 
correctly reproduced.
Apparently, H-atoms are not a plague and a curse, but the extensive use of 
restraints is a real disease of powder diffraction. Beside all other 
consequences, this pestilence diminishes the value of the method giving it 
a reputation of a speculative technique.


Don't restrain, be free!
Leonid

***
Leonid A. Solovyov
Institute of Chemistry and Chemical Technology
660049, K. Marx 42, Krasnoyarsk, Russia
http://sites.google.com/site/solovyovleonid
***

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Re: [sdpd] Re: Are restraints as good as observations ?

[xtal]

Leonid, I suggest you to try K4P2O7 - synchrotron data...

If you send me the data I may try.


OK.

K4P2O7 at room temperature is a good example for your horror museum of bad 
things done in the SDPD world and which could have been so much better if 
DDM was used.


This case belongs to the acentric class of problems. Acentricity leads to a 
2 times more unfavourable (atomic coordinates)/data ratio than for centric 
compounds. This is also the case for beta-Ba3AlF9 for which I can send the 
original 1993 data, if you wish, and you may see if Al-F distances are 
convincing without restraints using DDM (I obtained crazy Al-F distances in 
the 1.65-1.97 A range, instead of 1.81+-0.04 A for usually regular AlF6 
octahedra).


BTW, try to solve the structure before the Rietveld fif.

Best,

Armel

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