Re: [ccp4bb] Highest shell standards

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CCP4bb <-- 2007 <-- March 2007 <-- 26 March 2007

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Subject: SHARP question
From: artis {- at -} CHEMISTRY {- dot -} MONTANA {- dot -} EDU artis {- at -} CHEMISTRY {- dot -} MONTANA {- dot -} EDU
Date: 2007-03-26

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Subject: Re: Highest shell standards -oops-
From: "Edward A {- dot -} Berry" EABerry {- at -} LBL {- dot -} GOV
Date: 2007-03-26

Subject: Re: Highest shell standards
From: "Edward A {- dot -} Berry" EABerry {- at -} LBL {- dot -} GOV
Date: 2007-03-26

Actually I was thinking of a somewhat earlier paper:

Rayment,I. Molecular relacement method at low resolution:
optimum strategy and intrinsic limitations as determined
by calculations on icosahedral virus models.
Acta Crystallogr. A 39, 102 116 (1983).

But thanks for bringing the Caliandro et al. paper to my attention.
Thanks also to Fred. Vellieux for his comments, and to Pete Dunton
for explaining to me that while fft doesn't do fillin by default,
the 2MFo-DFc map coefficients from refmac5 do have fillin values
for the missing reflection, making model bias a problem when
many missing residues are included.

Now I understand Petrus's question.

Ed

Michel Fodje wrote:
> You are probably referring to the following works:
>
> Caliandro et al, Acta Cryst. D61 (2005) 556-565
> and Caliandro et al, Acta Cryst. D61 (2005) 1080-1087
>
> in which they used density modification to calculate phases for
> unmeasured reflections, and used the phases to extend the resolution by
> calculating rough estimates unmeasured amplitudes. Using this technique
> they actually could improve the electron density.
>
> If I'm not mistaken, George Sheldrick has implemented this "Free Lunch"
> algorithm in SHELXE.
>
> /Michel
>
> On Fri, 2007-03-23 at 08:05 -0800, Edward Berry wrote:
>
>>If instead you allow the missing F's
>>to "float", calculating them on each cycle from the previous map
>>using the fillin option, someone has shown (don't have the
>>reference handy at the moment) that the F's tend toward the true F's
>>(in the case that they weren't really missing but omitted as part
>>of the test).
>>
>>Ed

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CCP4bb <-- 2007 <-- March 2007 <-- 26 March 2007

Previous message:
Subject: SHARP question
From: artis {- at -} CHEMISTRY {- dot -} MONTANA {- dot -} EDU artis {- at -} CHEMISTRY {- dot -} MONTANA {- dot -} EDU
Date: 2007-03-26

Next message:
Subject: Re: Highest shell standards -oops-
From: "Edward A {- dot -} Berry" EABerry {- at -} LBL {- dot -} GOV
Date: 2007-03-26