Re: [ccp4bb] unbiased electron density map

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CCP4bb <-- 2008 <-- January 2008 <-- 09 January 2008

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Subject: Re: Sulfate ion on 2-fold axis
From: Dale Tronrud det102 {- at -} UOXRAY {- dot -} UOREGON {- dot -} EDU
Date: 2008-01-09

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Subject: Re: Principal axes and moment of inertia matrix
From: James Stroud jstroud {- at -} MBI {- dot -} UCLA {- dot -} EDU
Date: 2008-01-09

Subject: Re: unbiased electron density map
From: William Scott wgscott {- at -} CHEMISTRY {- dot -} UCSC {- dot -} EDU
Date: 2008-01-09

The map will be biased by whatever model is used to generate the phases.
If a heavy atom phasing method was used (MIR, MAD, etc) then at least you
do not have model bias.

A sigma-A weighted 2Fo-Fc map strives to have minimal bias, as does an
EDEN map with phase perturbation. However, minimally biased doesn't imply
negligible bias. A composite-omit 2Fo-Fc map made with simulated annealing
possibly comes the closest (apart from a heavy atom phased map).

HTH,

Bill

michael nelson wrote:
> In my understanding, unbiased electron density map usually refers to the
> Fo-Fc map.But I have seen in some papers sentences like that "The initial,
> unbiased 2FoFc map is contoured at".I was a bit confused since I was told
> by my instructor that the 2Fo-Fc was usually biased.
>
> Can anyone clear up this concept for me?
> Mike
>
>
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CCP4bb <-- 2008 <-- January 2008 <-- 09 January 2008

Previous message:
Subject: Re: Sulfate ion on 2-fold axis
From: Dale Tronrud det102 {- at -} UOXRAY {- dot -} UOREGON {- dot -} EDU
Date: 2008-01-09

Next message:
Subject: Re: Principal axes and moment of inertia matrix
From: James Stroud jstroud {- at -} MBI {- dot -} UCLA {- dot -} EDU
Date: 2008-01-09