[RMCProfile-users] G(r) from X-ray diffraction data

[Kaustuv Datta]

Dear Yuanpeng,

May I ask for a copy of the yet-to-be-released version of the package -- 
for both Win and Linux please, including the keywords. We have got some 
x-ray data to be tested.

Cheers,

Kaustuv



On 17.05.2018 16:57, Yuanpeng Zhang wrote:
> Hi Clemens,
>
> In the current public release of RMCProfile, it seems that we do have 
> some problems with the normalization for X-ray data due to the 
> q-dependent form factors. Therefore the normalization may not be so 
> straightforward as it is for neutron. Actually, if you have a look at 
> the manual in the section introducing the 'XRAY_REAL_SPACE_DATA' 
> keyword, you may probably notice that we have different options for 
> the normalization.
>
> I have ever looked at your attached pictures showing the problem you 
> described, but since the mailing list gets rid of the attachment so I 
> cannot see it now. So can I ask you to share with me (email: 
> zhangy3 at ornl.gov) your previously attached pictures? Also could you 
> please share with the whole folder in which you ran the RMCProfile so 
> I can have a look and see whether I can help solving the problem? 
> Thank you!
>
> Meanwhile, we are currently working on a new way for the X-ray data 
> fitting in RMCProfile, and in the new version we do the Fourier 
> transform internally in RMCProfile so we don't need to provide the 
> real space data by ourselves. The only thing we need is to provide the 
> reciprocal space data and give the program a keyword saying we also 
> want to fit in real space. The program now is not available to public 
> yet, but if you want to have a try, I can send the package to you (if 
> you tell me which operating system you are using).
>
> Cheers,
> Yuanpeng
>
>
> *Dr. Yuanpeng Zhang*
> Postdoctoral Research Associate
> Chemical and Engineering Materials Division
> Neutron Science Directorate
>
> Oak Ridge National Laboratory
> 1 Bethel Valley Road
> Bldg. 8600, Room C-509-C, Mailstop 6454
> Oak Ridge, TN 37831-6475
> Mobile | 865-335-4818
> Email | zhangy3 at ornl.gov <mailto:zhangy3 at ornl.gov> | Web | 
> aipeng1990.life <http://aipeng1990.life>
> On 05/15/2018 08:30 AM, Clemens Prescher wrote:
>> Hi there,
>>
>> i have problems figuring out how X-ray derived PDF should be correctly
>> inputted into RMCProfile.
>>
>> On page 157 in the RMCProfile manual it is written that the X-ray G(r)
>> needs to be normalised so that it is scaled from 0 to 1. This is exactly
>> the format i have. However, if I init my calculation and plot the 
>> "PDFs of
>> rmc fit" using rmcplot it has an offset (please see the attached 
>> figure "
>> gr_without_offset.ps")
>>
>> It is clear, that the RMC fit is actually normalized to 0 when going 
>> into
>> infinity.
>>
>> I thought, this might just a result by subtracting 1 from the 
>> previously 0
>> to 1 normalized G(r). But after several iterations using an offset of 
>> -1 it
>> became clear that low part is not normlized to -1. (see the
>> "gr_with_offset" figure attached).
>>
>> In the manual it is also written that G(r) goes from -(sum c_j b_j)² 
>> to 0.
>> But for X-ray this does not make sense due to q-dependent form 
>> factors...
>>
>> Can you please explain me how i should transform my data?
>>
>> Best wishes,
>> Clemens
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