> electron density for an atom with a B of 100 Angstroms**2 is so flat
> that you wonder how those atoms can be seen in electron density maps
Hmm....then there would not be any low resolution structures:
Say you have a low resolution structure, 3.5 A with a mean B of ~100A2 or
so.
Then on average all density peaks are broad and flat (FT of narrow SF=broad
ED). If you contour down correspondingly (in absolute terms), that looks
then just like a low resolution map. I see no problem there.
But you are right insofar as a 100A2 atom in a high resolution map -
properly contoured for that resolution - will not show much high level
density, consistent with no scattering contribution at high resolution. And
at very low density contour levels, the broad low-resolution density of that
atom may also be obscured in noise from the remaining high density
contributions.
Short of contour levels and noise issues, I can't see any contradiction or
problem here?
Best, BR
-----Original Message-----
From: Ronald E Stenkamp [mailto:[log in to unmask]]
Sent: Thursday, December 23, 2010 12:06 PM
To: Bernhard Rupp (Hofkristallrat a.D.)
Cc: [log in to unmask]
Subject: Re: [ccp4bb] Resolution and distance accuracies
Something related to the results in the 1984 paper, but never published, is
that the calculated electron density for an atom with a B of 100
Angstroms**2 is so flat that you wonder how those atoms can be seen in
electron density maps.
Ron
On Thu, 23 Dec 2010, Bernhard Rupp (Hofkristallrat a.D.) wrote:
>> can anyone point me to a more exact theory of distance accuracy compared
> to
>> optical resolution, preferably one that would apply to microscopy as
well.
>
> Stenkamp RE, & Jensen LH (1984) Resolution revisited: limit of detail in
> electron density maps. Acta Crystallogr. A40(3), 251-254.
>
> MX, BR
>
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