[Imgcif-l] ImgCIF Densiry Maps
Joe Krahn krahn at niehs.nih.govSat Mar 24 00:09:52 GMT 2007
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David Brown wrote: > Joe Krahn wrote: > >> What about equation forms? It is important to define more than just the >> space group, because non-standard settings can be useful in some cases. >> > The Hall symbol is a space group name (symbol) that specifies all > possible settings of the 230 regular space groups. It can easily be > expanded into the list of the expressions of symmetry operations. > I was looking over the Hall notation. If I understand it right, it only defines origin choices which are symmetry equivalents of the normal origin choice. There are cases where it is useful to shift a C2221 origin to align symmetry operators with those of P212121. I don't think the standard Hall notation handles this sort of case, at least not as tabulated in the International tables. The other issue is that interactions may need to define a specific symmetry operation. Is there a standard way to derive the symmetry operators in a specific order from Hall notation? Joe
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