Ivan, it might be helpful/instructive to have a look at this review on the subject you seem to be actively interested:
Acta Cryst. (2004). A60, 19-32. and some basic educational illustrations here: http://phenix-online.org/newsletter/CCN_2011_01.pdf (see "Electron density illustrations" article). Pavel On Wed, Nov 2, 2011 at 7:17 PM, Ivan Shabalin <shabali...@inbox.ru> wrote: > Hi James! > > Thank you very much for the gnuplot-ish version of ${CLIBD}/atomsf.lib!! > It works very nice and is very useful for education! > > As I understand, the form factor is the Fourier transform of electron > charge density. It is plotted as f(electrons) vs sin(tetta)/lambda and is > approximated as 5 Gaussian (Cromer and Mann) in REFMAC. And you made > reverse Fourier transform of the approximation and plotted the electron > density distribution in the real space. > > So, can I ask, what unit is x? Is it angstrom? > And what is Y? is it e/A3 (electron density)? > > I found, that at Bf=20, density profiles look almost the same for ions and > atoms (Mg2+ and Mg, Cl- and Cl). Does that means, there is no sense to > specify atomic charge in refmac refinement? It looks a bit strange, because > the numbers of electrons are different. Or decreasing in number of > electrons is compensated with significant decrease in atom size (that can > have the same effect as Bf lowering)? With Bf=0 the difference in curves is > significant. > > With best regards, > Ivan Shabalin >
