I think the question was not concerning right vs wrong space
group, but right vs a lower symmetry superset space group -
P4322 vs P43 for example. I would also be interested in
the answer.
At first glance it appears harder in the lower symmetry
because with each monomer you would be searching for a smaller
fraction of the contents of the AU. But if the rotation
function doesn't consider space group symmetry (?)
does that matter?
eab
Vellieux Frederic wrote:
> Ting-Wei Jiang wrote:
>> Dear experts,
>>
>> Sorry for a simple question but confusing me so much!
>>
>> Does it make bad effects on determining the number of identical
>> molecules in ASU by choosing low symmetry space group.
>> For example,If I choose lowest symmetry(p4) instead of higher
>> one(p43212).
>> Does it cause any trouble in determining structure while we try to
>> find the solution by molrep.
>> If molrep compare the patterson of observe and model in P1 space
>> group, it doesn't matter in choosing a lower s.g.?
>>
>> Any suggestion will be appreciated. Thanks in advance.
>>
>> Ting wei
>
> For molecular replacement: it does not matter if you carry out the
> rotation search in P422 or P43212. To understand this, ask youself the
> following question: what is the symmetry of the Patterson compared to
> that of the crystal? The symmetry of the Patterson is obtained from the
> symmetry of the crystal by converting all translation operators to the
> corresponding non-translation operators and adding a centre of symmetry.
> Hence for the rotation function, the symmetry of the Patterson will be
> P4/mmm for space group P422 and P4/mmm for P43212. Hence no difference
> for the rotation function.
>
> Different for P4 though: the symmetry of the Patterson there is P4/m.
>
> Hence the rotation function can be computed once for all space groups
> that have Patterson symmetry P4/mmm. No need to repeat the rotation
> function calculations several times.
>
> The situation is different for the translation function however. This is
> the stage at which you distinguish between all these space groups
> (including the pair of enantiomorphs P41212 and p43212). Failure to
> assign the proper space group cannot give you a satisfactory model.
>
> HTH,
>
> Fred.
>
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