Your understanding is correct, sigmaF values aren't required for
calculating electron density.
Many programs that calculate maps have an option to use the F/sigmaF
ratio to threshold the amplitudes used in map calculation - which would
require sigmaF. This isn't something I've seen used recently. The
presence of sigF is also sometimes used as a proxy for confirming that
the data is observed rather than calculated.
Pete
Francisco Hernandez-Guzman wrote:
> Hello everyone,
>
> My apologies if this comes as basic, but I wanted to get the expert’s take on whether or not the sigmaF values are required in the calculation of an electron density map. If I look at the standard ED equation, sigma’s don’t appear to be a requirement but all the scripts that I’ve looked at do require sigma values.
>
> I wanted to calculate the electron density for PDB id: 1HFS but the structure file only lists the Fo’s, Fc’s and Phases, but no sigmas. Would such structure factor file be considered incomplete?
>
> Thank you for your kind explanation.
>
> Francisco
>
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