George The CCP4 programs (I can't speak for others) involved with isomorphous replacement, i.e. scaling, FFT for difference Pattersons & Fouriers, and heavy-atom refinement (e.g. MLPHARE), mostly require that the native data and that of all the derivatives be not only in the same a.u. but sorted identically, so the preceding programs such as CAD go to a lot of trouble to ensure this.
Cheers -- Ian On 29 May 2012 14:29, George Sheldrick <gshe...@shelx.uni-ac.gwdg.de> wrote: > Which programs require that the data be the 'standard' a.u.? None of mine > require this. > > George > > > On 05/29/2012 03:44 PM, Ian Tickle wrote: >> >> Mark, thanks for pointing that out, I see it now: >> >> In P321 the only possible alternate indexing is (-h, -k, l): this is a >> 2-fold || c which is an operator of the hexagonal lattice but is not >> an equivalent reflection. >> >> The standard CCP4 a.u. is h = k, l>= 0 or h> k, k>= 0, so for >> example (3,2,1) would be in the standard a.u. (3> 2 and 2>= 0). In >> the alternate indexing this would be (-3, -2, 1); however it's >> impossible to transform this to the a.u. with any non-inverting >> equivalent. The only possibility is to invert the hand, i.e. to (3, >> 2, -1) which is again in the a.u.. >> >> So the required re-indexing operator to match (3, 2, -1) with (3, 2, >> 1) is (h, k, -l) which reindex won't allow without the LEFT keyword >> (and you would be well-advised to avoid doing it with phase columns!). >> >> Cheers >> >> -- Ian > > > -- > Prof. George M. Sheldrick FRS > Dept. Structural Chemistry, > University of Goettingen, > Tammannstr. 4, > D37077 Goettingen, Germany > Tel. +49-551-39-3021 or -3068 > Fax. +49-551-39-22582
