Re: [ccp4bb] units of f0, f', f''

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

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Subject: Re: about comparing Rwork and Rfree factors of different refinement trials
From: Dirk Kostrewa kostrewa {- at -} GENZENTRUM {- dot -} LMU {- dot -} DE
Date: 2010-02-26

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Subject: Re: units of f0, f', f''
From: Gerard DVD Kleywegt gerard {- at -} XRAY {- dot -} BMC {- dot -} UU {- dot -} SE
Date: 2010-02-26

Subject: Re: units of f0, f', f''
From: Bernhard Rupp br {- at -} RUPPWEB {- dot -} ORG
Date: 2010-02-26

Depends on in what units you want to get your electron density in, or what
scattering
objects (electrons) you integrate over for the SF formula. Since the
exponent
is dimensionless in the SF formula, and the FT commonly is electron density,

electrons (not negative charge) has to be somewhere in the SF formula.
If fo is in electrons, then f' and f" have to be units of electrons as well.
The f'
component reduces the real part scattering, it is negative (in electron
units, again not
in charge).

BR

-----Original Message-----
From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Tim
Gruene
Sent: Thursday, February 25, 2010 11:25 PM
To: CCP4BB@JISCMAIL.AC.UK
Subject: [ccp4bb] units of f0, f', f''

Dear all,

I just stumbled across the question about what is the unit of f' and f''.
The first couple of hits from ixquick.com claim it was e^-. Since e^- is not
a unit but symbolises an elemtary particle (of which fractions are
considered non-existent), I was wondering whether the unit of f, f', and f''
is actually e (a positive charge!) and the value of f^0 of Fe at its K-edge
was actually 26e or -26e - see e.g. Table 1 in
http://www.ccp4.ac.uk/courses/proceedings/1997/j_smith/main.html

Cheers, Tim

--
Tim Gruene
Institut fuer anorganische Chemie
Tammannstr. 4
D-37077 Goettingen

GPG Key ID = A46BEE1A

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

Next message:
Subject: Re: units of f0, f', f''
From: Gerard DVD Kleywegt gerard {- at -} XRAY {- dot -} BMC {- dot -} UU {- dot -} SE
Date: 2010-02-26