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R factor

  • Page ID
    19505
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    The term R factor in crystallography is commonly taken to refer to the 'conventional' R factor

    \(R =

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    \),

    a measure of agreement between the amplitudes of the structure factors calculated from a crystallographic model and those from the original X-ray diffraction data. The R factor is calculated during each cycle of least-squares structure refinement to assess progress. The final R factor is one measure of model quality.

    More generally, a variety of R factors may be determined to measure analogous residuals during least-squares optimization procedures. Where the refinement attempts to minimize the deviates of the squares of the structure factors (refinement against F2), the R factor based on F2 is used to monitor the progress of refinement:

    \(R(F^2) =

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    \).

    Likewise, refinement against I can be tracked using the Bragg R factor

    \(R_B =

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    \).

    Even for refinement against F2 or I, the 'conventional' R factor may be calculated and quoted as a measure of model quality, in order to compare the resulting quality of models calculated at different times and with different refinement strategies.

    The R factor is sometimes described as the discrepancy index.


    R factor is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Online Dictionary of Crystallography.

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