[phenixbb] Fwd: ML with Twinning?

[wtempel]

Hello,
please allow me to use this prompt for my twinning-related question.
A recent version of xtriage prints this warning:

It might be worthwhile carrying out refinement with a twin specific target
function.
Please note however that R-factors from twinned refinement cannot be
directly
compared to R-factors without twinning, as they will always be lower when a
twin law is used. You should also use caution when interpreting the maps
from
refinement, as they will have significantly more model bias.

Consider a case where specification of a twin law produces a “significant”
reduction in the residuals, say between 5 and 10%-points. Maps have not
revealed any additional features or model errors. Model geometry (such as
fraction of residues in favored regions of the Ramachandran plot) has not
improved. Should I specify the twin target during refinement?
How do my colleagues decide when to use twin refinement?
Best regards.
Wolfram Tempel

————— Forwarded message —————
From: Pavel Afonine pafonine at lbl.gov <http://mailto:pafonine@lbl.gov>
Date: Wed, Dec 16, 2015 at 2:06 PM
Subject: Re: [phenixbb] ML with Twinning?
To: “Keller, Jacob” kellerj at janelia.hhmi.org
<http://mailto:kellerj@janelia.hhmi.org>, “phenixbb at phenix-online.org”
phenixbb at phenix-online.org <http://mailto:phenixbb@phenix-online.org>

Hi Jacob,

Is Phenix able yet to use the ML target function with twinned data?
>
no.

Is it in the works?
>
There are formulas written out:

“Maximum likelihood refinement for twinned structures”:

http://phenix-online.org/newsletter/CCN_2011_01.pdf

some one needs to code it.

Pavel
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