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Hi.
I've found the discussion of significant digits and esds for
the unit cell constants very interesting, but the numbers you
listed from HKL2000 really got my attention. The last time
I had any faith in the esds for unit cell constants was 30 years
ago when working with stable, reproducible small molecule crystals.
We could center on high angle reflections, refine the unit cell
constants, and get esds with a precision of a part in 10,000.
When we did that, we were pretty proud of the precision, but I'm
not sure many believed the numbers were that accurate.
The values you report in your example are a part in 180,000,
and that's stupendous! Can you, or any of the other folks who
understand where the esds come from in HKL2000, explain why those
measurements are so much more precise now?
Thanks.
Ron
On Mon, 5 Jun 2006, Dunten, Pete W. wrote:
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Actually, if you use pdb_extract to prepare your deposition,
and for example have used HKL2000 for the integration and scaling,
you will get something like this, with esd's included -
_cell.length_a 87.453
_cell.length_b 146.925
_cell.length_c 189.787
_cell.angle_alpha 90.000
_cell.angle_beta 90.000
_cell.angle_gamma 90.000
_cell.length_a_esd 0.001
_cell.length_b_esd 0.002
_cell.length_c_esd 0.001
_cell.angle_alpha_esd 0.0
_cell.angle_beta_esd 0.0
_cell.angle_gamma_esd 0.0
_cell.volume 2438570.0
Wake up to the new world of mmcif! You can capture a lot more
information in your depostions now. See http://pdb-extract.rcsb.org/
All the best, Pete
David Borhani wrote
Marilyn,If you have post-refined the data (likely; default in HKL2000 &
mosflm), then you should have
standard deviations reported for the cell axes, e.g. a = 51.145 +/- 0.125
Angstrom. Since the
PDB doesn't have a way (that I know of) to report the SD . . .
