Tips and Tricks
P1 data collection / Pilatus
According to the classical paper (Z. Dauter (1999), Acta Cryst D55, 1703), the required rotation range for native data in space group P1 is 180°, and for anomalous data is 180° + 2 theta_max (theta is the diffraction angle). In the case of the standard geometry (direct beam vertical to, and central upon, the detector), this leads to 2-fold redundancy.
However, experience shows that collection of a few degrees more than that is a good idea, as the scaling will be more stable. So we regularly collect 200° for native data.
The Pilatus 6M detector at the SLS is composed of many panels, and therefore has horizontal and vertical dead areas. This generally lowers completeness, and the effect is particularly noticeable in P1. Untested idea: it may be good to make sure (if necessary, by moving the Pilatus) that the direct beam is not at a crossing between horizontal and vertical dead areas, nor at the middle of a panel (because this avoids that equivalent reflections suffer the same fate).
SAD/MAD data reduction
Run CORRECT twice, with STRICT_ABSORPTION_CORRECTION=TRUE and STRICT_ABSORPTION_CORRECTION=FALSE, and compare the results. I find that the anomalous signal in SeMet-SAD/MAD is significantly enhanced in the "Anomal Corr" and the "SigAno" disciplines with STRICT_ABSORPTION_CORRECTION=TRUE (which used to be the default in older versions but is not the default since Version May 8, 2007).
Example: 269 frames, 0.5°/frame, F222; STRICT_ABSORPTION_CORRECTION=TRUE
SUBSET OF INTENSITY DATA WITH SIGNAL/NOISE >= -3.0 AS FUNCTION OF RESOLUTION
RESOLUTION NUMBER OF REFLECTIONS COMPLETENESS R-FACTOR R-FACTOR COMPARED I/SIGMA R-meas Rmrgd-F Anomal SigAno Nano
LIMIT OBSERVED UNIQUE POSSIBLE OF DATA observed expected Corr
9.24 14085 4860 5073 95.8% 2.9% 3.5% 13978 26.78 3.7% 2.8% 66% 1.623 2115
6.59 24901 8560 8869 96.5% 4.6% 4.6% 24757 19.46 5.7% 5.5% 46% 1.356 3880
5.40 32411 11152 11422 97.6% 6.8% 6.6% 32194 14.14 8.4% 9.2% 28% 1.085 5121
4.68 37640 13022 13499 96.5% 6.7% 6.4% 37340 13.99 8.4% 10.0% 21% 1.017 5924
4.19 42764 14793 15307 96.6% 7.7% 7.2% 42425 12.59 9.5% 11.9% 19% 1.021 6746
3.83 48129 16600 16938 98.0% 11.4% 11.2% 47750 8.99 14.1% 18.6% 13% 0.914 7648
3.55 52640 18097 18333 98.7% 15.8% 16.1% 52229 6.61 19.5% 26.9% 10% 0.840 8384
3.32 56093 19557 19723 99.2% 24.3% 25.5% 55490 4.41 30.0% 42.9% 8% 0.781 8941
3.13 37869 18334 21008 87.3% 33.9% 36.3% 32035 2.33 43.6% 69.9% 6% 0.741 5214
total 346532 124975 130172 96.0% 9.5% 9.6% 338198 9.77 11.8% 18.8% 21% 0.964 53973
same data, STRICT_ABSORPTION_CORRECTION=FALSE (default):
SUBSET OF INTENSITY DATA WITH SIGNAL/NOISE >= -3.0 AS FUNCTION OF RESOLUTION
RESOLUTION NUMBER OF REFLECTIONS COMPLETENESS R-FACTOR R-FACTOR COMPARED I/SIGMA R-meas Rmrgd-F Anomal SigAno Nano
LIMIT OBSERVED UNIQUE POSSIBLE OF DATA observed expected Corr
9.24 14082 4858 5073 95.8% 3.0% 3.6% 13975 26.06 3.7% 2.9% 63% 1.530 2115
6.59 24893 8554 8869 96.4% 4.7% 4.7% 24749 19.08 5.8% 5.6% 42% 1.287 3876
5.40 32407 11147 11422 97.6% 6.8% 6.7% 32190 13.93 8.4% 9.2% 25% 1.035 5118
4.68 37631 13016 13499 96.4% 6.8% 6.5% 37331 13.76 8.5% 10.1% 16% 0.946 5915
4.19 42726 14775 15307 96.5% 7.8% 7.3% 42387 12.40 9.7% 12.1% 9% 0.889 6733
3.83 48125 16600 16938 98.0% 11.4% 11.2% 47746 8.89 14.2% 18.5% 3% 0.813 7646
3.55 52642 18095 18333 98.7% 15.8% 16.1% 52231 6.55 19.5% 26.7% 4% 0.773 8383
3.32 56102 19563 19723 99.2% 24.3% 25.6% 55499 4.39 30.1% 42.9% 3% 0.743 8943
3.13 37830 18318 21008 87.2% 34.9% 37.0% 31996 2.32 45.0% 70.5% 2% 0.709 5206
total 346438 124926 130172 96.0% 9.6% 9.7% 338104 9.62 11.9% 18.8% 15% 0.892 53935