From:   GORDON::COCKCROFT    "Jeremy Karl Cockcroft (Tel. 0171-631-6800)" 20-OCT-2000 15:11:35.13
To:     SMTP%"sianc.davies@bbsrc.ac.uk"
CC:     COCKCROFT
Subj:   Project: P2(1)/n refinement

Hi Sian,
  What you need to do here (and with P21/a also) is to distort the cell
by hand very slightly - you musn't start the beta angle at 90deg otherwise
you will either get a singular least-squares matrix or a very unstable one.
Try either slightly higher or lower - the two are actually equivalent, though
this may not be immediately obvious! Also do make sure that you start your
refinement with reasonable isotropic B values (say 0.5 for low T). Ditto with
P21/a (if you are using this in preference to P21/b z-axis unique).
  I hope this helps, Jeremy.

Back