Re: [ccp4bb] atomic scattering factors in REFMAC

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CCP4bb <-- 1999 <-- November 1999 <-- 30 November 1999

Previous message:
Subject: Re: atomic scattering factors in REFMAC
From: Ivan Shabalin shabalinig {- at -} INBOX {- dot -} RU
Date: 2011-11-03

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Subject: Re: atomic scattering factors in REFMAC
From: Pavel Afonine pafonine {- at -} GMAIL {- dot -} COM
Date: 2011-11-03

Subject: Re: atomic scattering factors in REFMAC
From: Pavel Afonine pafonine {- at -} GMAIL {- dot -} COM
Date: 2011-11-03

Ivan,

it might be helpful/instructive to have a look at this review on the
subject you seem to be actively interested:

Acta Cryst. (2004). A60, 19-32.

and some basic educational illustrations here:

http://phenix-online.org/newsletter/CCN_2011_01.pdf

(see "Electron density illustrations" article).

Pavel

On Wed, Nov 2, 2011 at 7:17 PM, Ivan Shabalin wrote:

> Hi James!
>
> Thank you very much for the gnuplot-ish version of ${CLIBD}/atomsf.lib!!
> It works very nice and is very useful for education!
>
> As I understand, the form factor is the Fourier transform of electron
> charge density. It is plotted as f(electrons) vs sin(tetta)/lambda and is
> approximated as 5 Gaussian (Cromer and Mann) in REFMAC. And you made
> reverse Fourier transform of the approximation and plotted the electron
> density distribution in the real space.
>
> So, can I ask, what unit is x? Is it angstrom?
> And what is Y? is it e/A3 (electron density)?
>
> I found, that at Bf=20, density profiles look almost the same for ions and
> atoms (Mg2+ and Mg, Cl- and Cl). Does that means, there is no sense to
> specify atomic charge in refmac refinement? It looks a bit strange, because
> the numbers of electrons are different. Or decreasing in number of
> electrons is compensated with significant decrease in atom size (that can
> have the same effect as Bf lowering)? With Bf=0 the difference in curves is
> significant.
>
> With best regards,
> Ivan Shabalin
>

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CCP4bb <-- 1999 <-- November 1999 <-- 30 November 1999

Previous message:
Subject: Re: atomic scattering factors in REFMAC
From: Ivan Shabalin shabalinig {- at -} INBOX {- dot -} RU
Date: 2011-11-03

Next message:
Subject: Re: atomic scattering factors in REFMAC
From: Pavel Afonine pafonine {- at -} GMAIL {- dot -} COM
Date: 2011-11-03