> 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:[email protected]] Sent: Thursday, December 23, 2010 12:06 PM To: Bernhard Rupp (Hofkristallrat a.D.) Cc: [email protected] 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 >
