diff options
Diffstat (limited to 'doc')
| -rw-r--r-- | doc/process_hkl.txt | 30 | ||||
| -rw-r--r-- | doc/twin-calculator.odt | bin | 18141 -> 18458 bytes | |||
| -rw-r--r-- | doc/twin-calculator.pdf | bin | 77383 -> 77052 bytes |
3 files changed, 3 insertions, 27 deletions
diff --git a/doc/process_hkl.txt b/doc/process_hkl.txt index 51742b3f..601bcaa2 100644 --- a/doc/process_hkl.txt +++ b/doc/process_hkl.txt @@ -19,36 +19,12 @@ crystal must be determined independently, with no information about its relationship to the orientation of crystals in other patterns (as would be the case for a rotation series of patterns). -The orientation of a crystal can be determined from the diffraction pattern only -within certain limits. For example, it is never possible, by geometry alone, to -distinguish between a diffraction pattern and its inverse, e.g. to tell the -[001] zone axis from [00-1]. That means that it is impossible to tell the -difference between a reflection and its Friedel opposite. If Friedel's Law is -not strictly observed, as is the case for data showing anomalous effects, and if -we wish to measure the anomalous differences, then another way to distinguish -the orientations apart must be determined. - -So far, there is no such method which works reliably. You will need to take -this into account when deciding how to merge the data. - -Because of the above, the use of symmetry in serial crystallography is -"backwards" with respect to the method in conventional crystallography. If you -are not interested in distinguishing between any of the possible ambiguities, -then you would just treat ambiguous reflections as equivalent and merge them -together in a high-symmetry point group. If you needed to distinguish between -them, then you would merge into a lower symmetry. - -Having first determined the point group for the structure under examination, -decide whether or not you need to tell Friedel opposites (Bijvoet pairs) apart. -If not, merge according to the Laue class corresponding to the point group. The -Laue class is just the point group after introducing a centre of symmetry. The -point group is equivalent to the Laue class if the structure is centrosymmetric. - Some Laue classes are merohedral. This means that the orientation will have an -additional ambiguity, but this time more serious. The two (or more) possible +ambiguity, but this time more serious. The two (or more) possible orientations could be called "twins", but the mechanism of their formation is somewhat different to the conventional use of the term. In these cases, you -will need to merge according to the corresponding holohedral Laue class. +will need to merge according to the point group corresponding holohedral Laue +class. The document twin-calculator.pdf contains more detailed information about this issue, as well as tables which contain all the required information. diff --git a/doc/twin-calculator.odt b/doc/twin-calculator.odt Binary files differindex 89708e46..500052bb 100644 --- a/doc/twin-calculator.odt +++ b/doc/twin-calculator.odt diff --git a/doc/twin-calculator.pdf b/doc/twin-calculator.pdf Binary files differindex 625565f8..0e4b66aa 100644 --- a/doc/twin-calculator.pdf +++ b/doc/twin-calculator.pdf |