Centric and acentric reflections: Difference between revisions

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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> ) (would be nice to have little plots here).
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 ==
1,330

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