Okay, thanks for the correction/elaboration. I love the CCP4BB for this reason!
Jacob -----Original Message----- From: Phil Jeffrey [mailto:pjeff...@princeton.edu] Sent: Thursday, September 08, 2016 5:15 PM To: Keller, Jacob <kell...@janelia.hhmi.org>; CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Help with MR and self rotation function Since the systematic absences in I2x2x2x are (h+k+l=2n), if you're looking at a single plane through reciprocal space with one constant index would show every other reflection missing so you might expect to see the sort of diamond pattern you get with C2 etc. The lattice appears to be non-orthogonal since it's non-primitive orthogonal. Some bad ASCII art that some mail programs might mangle: a*b* plane l=even a*b* plane for l=odd X . X . X . X . X . . X . X . X . X . X X . 0 . X . X . X . . X . X . X . X . X X . X . X . X . X . X=visible, 0=visible and h=k=0, . = systematic absence The pattern alternates because of the 2n dependency on all three indices. For C2, incidentally the a*b* plane shows the same pattern for all l since the systematic absence is (h+k=2n) For cubic the face diagonals would be perpendicular since a=b=c but for orthorhombic that's generally not the case - so it does not superficially look orthorhombic. The images appear to show fairly significant diffuse scattering and perhaps a weak second lattice. While not ideal I don't view it as obviously pathological. I've used worse. Phil Jeffrey Princeton On 9/8/16 2:51 PM, Keller, Jacob wrote: > I saw in the second image some spots on an apparently non-orthogonal > lattice, which I don’t think can happen with 222 symmetry, since the > angles must all be 90 deg. Perhaps the I-centring affects this, but I > don’t think so (please correct me if this is wrong.) If these angles > are indeed not 90 deg, then, the space group cannot be what you think it is. > > There are also a bunch of doubled spots, which can present problems. > > JPK >
