[RMCProfile-users] [EXTERNAL] Using gpar_to_tot_gen

[Zhang, Yuanpeng]

Hi All,

First, thanks a lot Dave for pointing that out! I should have been more clear about the normalization.

Second, the gpar_to_tot_gen program sums partial PDFs, following Eqn. 17 in the paper mentioned by Dave, in which case our normalization factor is the FZ coefficient, i.e. $\langle \bar{b}\rangle^2$ or $(\sum_ic_ib_i)^2$ (LaTeX formatted equation).

Cheers,
yuanpeng

-----Original Message-----
From: rmcprofile-users <rmcprofile-users-bounces at shadow.nd.rl.ac.uk> On Behalf Of David Keen - UKRI STFC via rmcprofile-users
Sent: Friday, May 29, 2020 11:49 AM
To: rmcprofile-users at shadow.nd.rl.ac.uk
Cc: David Keen - UKRI STFC <david.keen at stfc.ac.uk>
Subject: Re: [RMCProfile-users] [EXTERNAL] Using gpar_to_tot_gen

The normalization factor depends on the definition of the total PDF that you want to calculate.  For one definition it is simply "1", for another it is <b>^2...see J. Appl. Cryst. (2001) 34 172.  But there is a subtlety here as it depends whether the weighted partial PDFs are added together or whether the weighted (partial PDFs - 1) are added together (c.f. Eqtns 17 and 10 in the reference).  I haven't used the program (but plan to now I know that it exists!) so I don't know which version of the summation is used, so I advise that the output is checked carefully!

Best wishes
Dave

On 29/05/2020, 16:22, "rmcprofile-users on behalf of Zhang, Yuanpeng via rmcprofile-users" <rmcprofile-users-bounces at shadow.nd.rl.ac.uk on behalf of rmcprofile-users at shadow.nd.rl.ac.uk> wrote:

    Sorry, I forgot the normalization factor in the coefficient, which is actually the sum of the coefficient for all pairs, i. e. the Faber-Ziman coefficient.
    
    Cheers,
    yuanpeng
    
    -----Original Message-----
    From: rmcprofile-users <rmcprofile-users-bounces at shadow.nd.rl.ac.uk> On Behalf Of Sumit Khadka via rmcprofile-users
    Sent: Wednesday, May 27, 2020 12:48 AM
    To: rmcprofile-users at rmcprofile.org
    Cc: Sumit Khadka <sumitkhadka08 at gmail.com>
    Subject: [EXTERNAL] [RMCProfile-users] Using gpar_to_tot_gen
    
    Hello,
    
    I apologize if this question has been asked already.
    
    I am trying to calculate theoretical PDF by using gpar_to_tot_gen program.
    I already have my partial PDF files as well.The use of this program requires knowledge of the scattering coefficients corresponding to each pair of atoms , eg for SF6, one coefficient each corresponding to S-S, S-F, and F-F pairs.
    
    Does the scattering coefficient for the bond mean the Faber-Ziman weighting coefficients calculated as (C_a * C_b * B_a * B_b)/ <B>^2 where C_i is the concentration of atom i, B_i is the scattering length of atom i and <B> represents the average scattering length of all the atoms involved?
    
    Thanks,
    Sumit Khadka
    University of Houston, Houston, TX
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