Bernhard The term "enantiomorphic pair" is used consistently in ITC-A to mean one of the 11 pairs of what you previously called "chiral space groups". PersonalIy I would never use the term "chiral" in this context even though it is synonymous with "enantiomorphic" (I would reserved "chiral" for single objects like hands, screws, mollusc shells and molecules - actually pretty well everything in Nature is chiral, natural achiral objects are in the minority).
You say "Thou shalt not use those descriptors for SGs, only for structures" but enantiomorphic in the sense above is being used in ITC-A exactly to describe a SG, so on which tablet of stone is this commandment inscribed? Certainly not in ITC. Also on my CCP4 web page that I referred to earlier I used "enantiomorphic" to describe a structure (or to be precise a crystal), not a SG (43 "enantiomorphic" SGs are not enantiomorphic if it refers to the SG). I accept that nowhere does ITC use "enantiomorphic" in the way I'm using it but you wanted a suitable descriptor and I don't see any alternative candidates. As you said the only distinction ITC makes is between centrosymmetric and non-centrosymmetric (presumably having centrosymmetry leads to great simplication of the structure-factor equations in that you only have to worry about 2 alternative values for the phase), but that's not the description you're seeking for the reasons you gave. The only apparent inconsistency here is that the same adjective is being used to describe two different things. But is that really an inconsistency? Can't I use "black" to describe both crows and blackboards? Cheers -- Ian On 29 April 2014 10:32, Bernhard Rupp <hofkristall...@gmail.com> wrote: > Hi Fellows, > > I have bugged now the ultimate authorities including Howard Flack (of > Flack parameter fame), > and alas, there is no official descriptive adjective for these 65 Söhnke > space groups. > Chiral is definitely wrong, and so is enantiomorphic, although 22 of the > nameless form 11 > enantiomorphic pairs. Thou shallst not use those descriptors for SGs, only > for structures. > > So the contest for a proper descriptive adjective is still open. > > Best, BR > > PS: Otherwise it is a bit like saying 'You know, that thing, the one where > you see stuff moving and > it is not black and white' instead of simply 'color TV' <- almost as old > as space groups.... >
