Re: [sdpd] thermal Biso

[Akhilesh <tripathi.a...@gmail.com>]

Dear Alaoui:

There are several ways to look into this problem and you have to check all
possibilities.

First of all, I presume you are not refining the thermal parameters and
occupancy together, they are highly co related.

A high  isotropic B indicate too much scattering for that atomic site, that
means either the occupancy is more than adequate or the atomic species or
oxidation state is wrong. It is a good idea to see if your model makes
chemical sense with the current set of atomic species. Look for bond
lengths, bond angles and overall structure. Is this reasonable? Have similar
structure, bond lengths and angles been reported in past?

Now is this lab data? Check your no. of refinable parameters and observed
data. It should be at least three and preferably five. More the merrier. The
idea is you should not be over fitting your data (for example shawdowing a
horse with an elephant)
There are more such things to check.

But if you think all these things are reasonable then start fresh again with
some constraints and restraints such as bond length and angle and may be
even chemical constraints.

Also in your structure you can  look if you can tie same set of atomic
species together into one group for example in a zeolite structure all
framework atoms can be tied to one Biso group and all non framework species
can be tied to another group with another Biso. All these constrains can
be slowly released towards the end depending upon how good was the
refinement. Also try your variables slowly.

So Azis try few of these things and see what happens.
I am sure there can be more comments from experts about all these things.

Best regards
Akhilesh Tripathi



On 11/7/06, alaoui aziz <az_alaoui...@yahoo.fr> wrote:
>
>   Dear all,
> I am trying to refine the structure of a new iron phosphates using the
> programm Fullprof.
> the problem is that the thermal parameter Biso are very high und
> unsignifiant.
> can anybode help me what I should do to solve this problem.
> Thank you in advance.
> All best wishes!
>
>
> ---------------------------------
> Découvrez une nouvelle façon d'obtenir des réponses à toutes vos questions
> ! Profitez des connaissances, des opinions et des expériences des
> internautes sur Yahoo! Questions/Réponses.
>
> [Non-text portions of this message have been removed]
>
> 
>


[Non-text portions of this message have been removed]



 
Yahoo! Groups Links

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

<*> Your email settings:
    Individual Email | Traditional

<*> To change settings online go to:
    http://groups.yahoo.com/group/sdpd/join
    (Yahoo! ID required)

<*> To change settings via email:
    mailto:sdpd-digest...@yahoogroups.com 
    mailto:sdpd-fullfeatured...@yahoogroups.com

<*> 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/