Low Temp refinement.

Gerard 'CD' Kleywegt GERARD at XRAY.BMC.UU.SE
Thu Apr 11 12:19:24 EST 1996


>The coordinates of the warm model were in Ang. units.  When they were 
>transformed into fractional coords in the new cell, they were about an Ang.
>away from where they should be.

fractionalisation followed by re-orthogonalisation is *not* a good
way to transfer model coordinates from one cell to the next in
the case of (even slightly) different cell constants
there is no "law of conservation of fractional coordinates" ;-)
much more likely is a slight rearrangement (small rot + trans)
which can usually be fixed with rigid-body refinement
apart from that: re-orthogonalising in a different cell will
give systematic errors in all your bond lengths; if your new
cell is smaller than the old one, you're effectively shrinking
your entire molecule ! (the determinant of the product matrix
is non-unity)

just my 2 oere worth

--gerard



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