Dear Hailiang,As James said, the hermitian symmetry of Fourier coefficients,
F(h)=F*(-h), that is known in diffraction theory as the Friedel's law, is an
equivalent of the condition that the corresponding function (electron density)
is a real function.I think if you need further information you can make a look
into some basic textbook or write me (or to somebody on your choice :-) a
direct personal mail; I am not sure if we need to bother the whole community by
further details of this discussion. You can write and send to CCP4bb the resume
afterall if you want.Best regards,SachaDe: James Holton <jmhol...@lbl.gov>>
Uhh. No. You will only get "imaginary" electron > density if your structure
factors violate Friedel's law. I am not aware of > map calculation codes that
do this (on purpose).> > Yes, I think Fourier synthesis at a finite resolution
range > will generate some negative, or more generally imaginary values in real
> space (hope I am right again:).
