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Centric and acentric reflections: Difference between revisions
→Reciprocal space
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Centric reflections in space group P2 and P2<sub>1</sub> are thus those with 0,k,0. There exist space groups without centric reflections, like R3. | Centric reflections in space group P2 and P2<sub>1</sub> are thus those with 0,k,0. There exist space groups without centric reflections, like R3. | ||
Properties: centric reflections have only two phase possibilities, e.g. 0° and 180° (but in any case 180° apart), and centric reflections do not have an anomalous signal (can these properties be easily derived here?). Furthermore, the "intensity statistics" of centric reflections | Properties: centric reflections have only two phase possibilities, e.g. 0° and 180° (but in any case 180° apart), and centric reflections do not have an anomalous signal (can these properties be easily derived here?). | ||
(<math> P(|E|) = 2 |E| e^{-|E|^2} </math> ) are different from those of acentric reflections | |||
(<math> P(|E|) = \sqrt{\frac{2}{\pi}} e^{-|E|^2/2} </math> ) ( | Furthermore, the "intensity statistics" of centric reflections | ||
(<math> P(|E|) = 2 |E| e^{-|E|^2} </math> ) | |||
<gnuplot> | |||
set xrange [0:5] | |||
plot 2*x*exp(-x*x) | |||
</gnuplot> | |||
are different from those of acentric reflections | |||
(<math> P(|E|) = \sqrt{\frac{2}{\pi}} e^{-|E|^2/2} </math> ) | |||
<gnuplot> | |||
set xrange [0:5] | |||
plot sqrt(2/3.14)*exp(-x*x/2) | |||
</gnuplot> | |||
. | |||
Centric reflections have a special role in experimental [[phasing]]. | Centric reflections have a special role in experimental [[phasing]]. | ||
== References == | == References == | ||