question about MAD

yuanping yuanping at
Fri May 30 10:13:07 EST 2003

Dear Dr. Merritt,
Thank you very much for clarify this conception for me. I have another
related question. " How to get the phase for F(real) and F(imaginary)? "
>From text book, " The phases of F(real) and F(imaginary) depend only on the
position of the heavy atom in the unit cell, so once the heavy atom is
located by patterson methods, the phases can be computed" ( Crystallography
made crystal clear). But how?  As F(imaginary) is always perpendicular to
F(real), determining the  phase of either F( real) or F(imaginary) will
automatically give us the other. But how to link the phase of heavy atom to
them? Is that the phase of heavy atom just the phase of combined
contribution vector of F(real) and F(imaginary)? or just the F(real)...
Thanks again,

"Ethan Merritt" <merritt at> wrote in message
news:bb6kf2$mtp$1 at
> In article <3ed6d0cc$1 at>,
> yuanping <yuanping at> wrote:
> >Dear colleagues,
> >I have a question about MAD. Is there any relationship between f' and f''
> >got by fluorescence scan and Fr and Fi used to calculate the anomalous
> >structure factor? Thanks.
> F(real) = f'  and F(imaginary) = f"
> This isn't "used to calculate" the anomalous scattering factor;
> it *IS* the anomalous scattering factor.
> See tutorial at
> --
> Ethan A Merritt

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