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Re: [ccp4bb] just how bad can phases be and still help
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CCP4bb <-- 1999 <-- November 1999 <-- 30 November 1999
Previous message:
Subject: Re: display a map from a quantum chemical calculation
From: Warren DeLano warren {- at -} DELSCI {- dot -} COM
Date: 2007-09-08		Next message:
Subject: display a map from a quantum chemical calculation
From: William Scott wgscott {- at -} CHEMISTRY {- dot -} UCSC {- dot -} EDU
Date: 2007-09-08


Subject: Re: just how bad can phases be and still help
From: Victor Lamzin victor {- at -} EMBL-HAMBURG {- dot -} DE
Date: 2007-09-08

James Holton wrote:
>
>
> Perhaps the best way to settle this is to put it out to a challenge:
> does anybody have a map calculated with an average
> FOM(fromsomeprogram) < 0.5 that they were able to trace?
I saw ARP/wARP iteratively tracing such densities if the resolution was
1.5 A or higher - a bit subjective answer, I suspect.

If the resolution is 1.0 A or higher then ab-initio or semi-ab-initio
programs (e.g. ACORN) can recover a structure from a value of FOM close
to zero - again, only iteratively.
> Does anyone have a map calculated with FOM(fromsomeprogram) > 0.5 that
> was total garbage?
Yes, a lot. Two simple examples are:

Type 1: lack of strong low angle reflections (e.g. due to overloads).
Even for a FOM value approaching 1.0 the map would hardly be
interpretable. More general case is the data having bad Wilson plot.
Type 2: pathological cases with 60 degrees phase error (FOM 0.5) to each
of the two enantiomorphs, left and right-hand MIR solutions, similar SAD
cases (60 degrees to the correct phases and 60 degrees to those for the
'babinet-sign-inverted' map).

Victor

CCP4bb navigation

CCP4bb <-- 1999 <-- November 1999 <-- 30 November 1999
Previous message:
Subject: Re: display a map from a quantum chemical calculation
From: Warren DeLano warren {- at -} DELSCI {- dot -} COM
Date: 2007-09-08		Next message:
Subject: display a map from a quantum chemical calculation
From: William Scott wgscott {- at -} CHEMISTRY {- dot -} UCSC {- dot -} EDU
Date: 2007-09-08
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