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R-factors: Difference between revisions
add R_d which measures radiation damage
(add R_d which measures radiation damage) |
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Weiss and Hilgenfeld <ref name="WeHi97">M.S. Weiss and R. Hilgenfeld (1997) On the use of the merging R-factor as a quality indicator for X-ray data. J. Appl. Crystallogr. 30, 203-205[http://dx.doi.org/10.1107/S0021889897003907]</ref>). | Weiss and Hilgenfeld <ref name="WeHi97">M.S. Weiss and R. Hilgenfeld (1997) On the use of the merging R-factor as a quality indicator for X-ray data. J. Appl. Crystallogr. 30, 203-205[http://dx.doi.org/10.1107/S0021889897003907]</ref>). | ||
==== measuring quality of averaged intensities/amplitudes ==== | |||
for intensities use | for intensities use | ||
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In the sums above, the summation omits those reflections with just one observation. | In the sums above, the summation omits those reflections with just one observation. | ||
==== measuring radiation damage ==== | |||
We can plot (Diederichs <ref name="Di06">K. Diederichs (2006). Some aspects of quantitative analysis and correction of radiation damage. Acta Cryst D62, 96-101 [http://strucbio.biologie.uni-konstanz.de/strucbio/files/Diederichs_ActaD62_96.pdf]</ref>) | |||
<math> | |||
R_{d} = \frac{\sum_{hkl} \sum_{|i-j|=d} \vert I_{hkl,i} - I_{hkl,j}\vert}{\sum_{hkl} \sum_{|i-j|=d} (I_{hkl,i} + I_{hkl,j})/2} | |||
</math> | |||
which gives us the average R-factor of two reflections measured d frames apart. As long as the plot is parallel to the x axis there is no radiation damage. As soon as the plot starts to rise, we see that there's a systematical error contribution due to radiation damage. | |||
Strong wiggles at very high d are irrelevant as only few reflections contribute. | |||
=== Model quality indicators === | === Model quality indicators === | ||