[phenixbb] individual anisotropic adps
pafonine at lbl.gov
Thu Dec 11 08:24:00 PST 2008
from what I recall is if you refine anisotropic ADP at "too low"
resolution in other refinement programs, they were often stopping
complaining about non-positive definite U or unstable refinement. This
seemed to me the main technical limit.
In phenix.refine this does not happen but it doesn't mean that refining
anisotropic ADP at "too low" resolution will yield meaningful results.
I'm not sure that there is an exact resolution borderline for doing (or
not doing) individual anisotropic ADP refinement. From my experience,
I've never seen a case at ~1.5A and higher where switching from iso- to
anisotropic model was not good. Then this question transforms into "at
which resolution you start refining waters as anisotropic?"... A very
rough number I would say is 1.2-1.1A and higher.
In-between 1.5 and 1.7 (1.8A) is a "gray zone", where it is very likely
that anisotropic ADP refinement will result in over-fitting, however
there is a chance that it might still be valid.
Summarizing, if I have a data at resolution between between 1.5 and 1.8A
resolution, I just try two refinements: in one refining isotropic and in
another refining anisotropic ADPs. Rfree is your best friend here (and
Rfree-Rwork). In my opinion, this is the most robust and cheep way to
get the answer.
On 12/11/2008 7:48 AM, gerwald jogl wrote:
> Hi All,
> I was wondering if there is information/recommendations out there for
> the resolution required to refine individual anisotropic adps. I think
> the recommendation for shelx is at least 1.5 A resolution.
> In addition, is phenix set up and would it make sense to combine tls
> with individiual anisotropic adps?
> All comments welcome,
> phenixbb mailing list
> phenixbb at phenix-online.org
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