Hi.
Non-crystallographic symmetry (NCS) doesn't apply to the entire crystal, so how can it give rise to systematic absences? I know it can give rise to systematically weak classes of reflections, but they aren't entirely absent.
Ron
On Thu, 11 Dec 2008, Winter, G (Graeme) wrote:
> One of the many facilities in pointless is to search for absences and provide a list of likely spacegroup choices based on the results. It includes adjustments for neighbouring spots to address one of Eleanor's concerns. NCS can cause reflections to be systematically absent too.
>
> The program can be found on the ccp4 prerelease pages or on the pointless ftp site.
>
> Cheers,
>
> Graeme
>
> -----Original Message-----
> From: CCP4 bulletin board [mailto:[log in to unmask]] On Behalf Of Eleanor Dodson
> Sent: 11 December 2008 09:41
> To: [log in to unmask]
> Subject: Re: [ccp4bb] About system absence in P4222?
>
> 劉家欣(NTHU) wrote:
>> Dear All:
>>
>> We have a crystl with P4222 sg.
>> All statistics look fine.
>> However, there is a system absense in l axis.
>> Any body have experiences on that?
>> Any suggestions would be high appreciated.
>>
>> jaishin
>>
> can you give more details, eg all reflections along the particular axis..
> Things like ice rings or overlapping intensity from a next neighbour getting integrated inapropriately can cause anomalies..
> Eleanor
>
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