Ibrahim M. Moustafa wrote:
The last question: In the same paper, for the complex structure R and
Rfree are equal (30%) is that an indication for improper refinement in
these published structure? I'd love to hear your comments on that too.
Several times I solved low resolution structures using high resolution
models, and noticed that R-free increased during atomic positional
refinement. This could be expected from the assertion that after
refinement to convergence, the final values should not depend on
the starting point: If I had started with a crude model and refined
against low resolution data, Rfree would not have gone as low as the
high-resolution model, so if I start with the high resolution model
and refine, Rfree should worsen to the same value as the structure
converges to the same point.
Thinking about the main purpose of the Rfree statistic, in a very
real way this tells me that the model was better before this step
of refinement, and it would be better to omit the minimization step.
Perhaps this is what the authors did.
On the other hand it does not seem quite right submit a model that
has simply been rigid-body-refined against the data- I would prefer to
refine to convergence and submit the best model that can be supported
by the data alone, rather than a better model which is really the model
from a better dataset repositioned in the new crystal.
Ed
