[phenixbb] individual anisotropic adps

Pavel Afonine pafonine at lbl.gov
Thu Dec 11 08:24:00 PST 2008

Hi Gerwald,

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,
> Gerwald
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