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Re: [sdpd] error measurements
This - and indeed those that have come before - is a very interesting point
of view. The storing of the whole diffraction pattern with a crystal
structure is of course impossible with the current file formats of the
Cambridge Structural Database, so I'm very happy with the view, but not
happy to have to say that at the moment it is impossible to realise it !
That's not to say that it won't be possible at some time in the future ...
This is all very valuable and helpful information for us - please keep it
coming.
Cheers,
Steve Maginn
At 10:02 23/01/01 -0600, you wrote:
>
>
>The pain with background substraction CAN be that you have high values
>with a further 'perfect' fit. In my experience this has often to do the
>presence of a relative large amount of peaks with low intensity. You may
>argue that you should measure longer under these circumstances, or reduce
>the 2 theta angle you are using. Even so, the improvement is minor if you
>have a low symmetry structure with atoms having very different scattering
>factors (heavy metal oxides for instance). And yes your Rwp might than be
>more an indication of how good the back ground has been fitted. High
>background level gives a nice and low Rwp. With this in mind I think that
>at the moment of writing there is no proper figure of merit for a Rietveld
>refinement, and yes the diffraction pattern should be available. I am sure
>that Steve Maginn is happy with this view :-).
>
>By the way I assume that the background is never substracted in the Rwp
>unless stated otherwise.
>
>Best wishes
>
>
>Jaap
>
>
>Jaap Vente
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>
=====================================================
Dr. Stephen J. Maginn,
Support and Marketing Manager,
Cambridge Crystallographic Data Centre (CCDC),
12 Union Road,
Cambridge CB2 1EZ, UK
phone +44 (0)1223 762534
FAX +44 (0)1223 331116
e-mail maginn...@ccdc.cam.ac.uk
http://www.ccdc.cam.ac.uk
=====================================================