[cctbxbb] Introducing arbitrary translations in symmetry operations

Emre S. Tasci emre.tasci at ehu.es
Fri Jun 3 03:49:04 PDT 2011

Dear Ralf,

Thank you very much for your answer. What we are actually trying to do 
is to refer to the tables of ITA (2006) 15.2.1.* where you have your 
space group & additional generators and voila! It's not the normalizers 
defined as a group but the group+normalizers defined as a new group.. 8)

Here is yet another question-- I might be missing something obvious here 
so you got my apologies beforehand if it proves that I do:

Take for instance SG #16, P222. I add the 3 translation operators
plus the inversion:

then I get  SG #47, Pmmm with (2*b,2*c,2*a) -- but why not 
(2*a,2*b,2*c)? As I said, I'm highly suspecting that I'm missing 
something very very obvious but at this moment I'm baffled.

With my best regards,

On 06/02/2011 07:32 AM, Ralf W. Grosse-Kunstleve wrote:
>> But we couldn't find a way to introduce "x,y,z+t" while we are "expand_smx"ing the space group with these operators.
> The space_group class only supports finite groups (and only in settings
> that can be represented with integral rotation parts and rational
> translation parts).
> We have the class cctbx.sgtbx.search_symmetry, which multiplies the
> discrete origin shifts into the space group and keeps track
> of the continuous allowed origin shifts separately.
> It would need new code to determine a full description of affine
> normalizers. (Are they considered space groups?)

Emre S. Tasci - http://www.emresururi.com
Fisica de la Materia Condensada
Facultad de Ciencia y Tecnologia
Universidad del Pais Vasco
Apartado 644
48080 Bilbao / Spain

More information about the cctbxbb mailing list