[RMCProfile-users] Unusual BROADENING_CORRECTION :: bug?

[SUMMER, ARON (PGR)]

Hi Yuanpeng,

Thank you for your prompt response! I have attached a zip folder of one of my runs displaying the oddity in question. In the same folder is a .png image displaying the odd feature (in case everything looks normal once you investigate the folder).

I have done a little investigation myself and another RMCProfile run with the same files, but slightly different resolution and broadening values (listed below) does not display the feature.
  > RESOLUTION_CORRECTION :: 0.021
  > BROADENING_CORRECTION :: 0.0065125

I generally run my simulations with a higher low r weighting, but have left the "BROADENING_CORRECTION ::" disabled for the first PDF weighting the low r, see the full r range for the feature described.

Kind regards,
Aron Summer

________________________________
From: Zhang, Yuanpeng <zyroc1990 at gmail.com>
Sent: 28 October 2020 15:51
To: rmcprofile-users at shadow.nd.rl.ac.uk <rmcprofile-users at shadow.nd.rl.ac.uk>; rmcprofile-users at rmcprofile.org <rmcprofile-users at rmcprofile.org>
Cc: SUMMER, ARON (PGR) <A.Summer at warwick.ac.uk>
Subject: Re: [RMCProfile-users] Unusual BROADENING_CORRECTION :: bug?

Hi Summer,

This broadening feature is implemented by myself to kind of mimick the Qbroad parameter in pdffit community, to deal with the broadening effect in real space as the result of increasing noise level as approaching high Q.

I am happy you grab this feature and test it since to make it useful, we do need a robust test from user community.

So, concerning your report, I did a quick test with 'ex_1'  in RMCProfile package. I did try using either a small value (0.008) for the broadening and comparing the resulted pattern with that without broadening. As far as I see, I did not see any obvious problems as you described - refer to the link below for a screenshot.

https://u.pcloud.link/publink/show?code=XZvCHHXZ8s3Rb63jF5J5cqsaQrVykYt84yu7

Maybe it can be helpful if you can share with me your whole RMC folder so I can help inspecting what the problem may be (or whether indeed we have a problem there).

Cheers
Yuanpeng

--

Dr. Yuanpeng Zhang
Computational Instrument Scientist
Spallation Neutron Source

Oak Ridge National Laboratory
1 bethel valley road, Oak Ridge, TN 37830, US
Mobile: +1(865)-335-4818
Email: zhangy3 at ornl.gov | Web: https://www.iris2020.net <https://www.iris2020.net/>

On 10/28/20, 11:03 AM, "rmcprofile-users on behalf of SUMMER, ARON (PGR) via rmcprofile-users" <rmcprofile-users-bounces at shadow.nd.rl.ac.uk on behalf of rmcprofile-users at shadow.nd.rl.ac.uk> wrote:

    Hi,

    Just reporting what I believe to be a bug with the "BROADENING_CORRECTION ::" function.

    I've recently upgraded to RMCProfile v 6.7.8 in the hopes that the BROADENING_CORRECTION could solve some slight peak broadness mismatches I was experiencing. While including this term I noticed some unusual behaviour of the "baseline" of the RMC fit when using values below 0.01. In the G(r) fit the low r region of the baseline had a negative curve to it which abruptly truncates at my minimum atom-atom distances, this curve is present in the initial system and after having been run for a period of time (although hidden under broad peaks, the cut-off is still very visible in the G(r).

    I have checked the same system without the BROADENING_CORRECTION keyword (to check if it's something else in 6.7.8) and with a value above 0.01 and this feature is only present when BROADENING_CORRECTION is set to below 0.01 in my experience.

    Racked my mind on why a peak broadening function would change an absolute baseline and came up blank, so figured it was probably a bug in the code.

    Please let me know if you want me to send across my setup files.

    Kind regards,
    Aron Summer
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