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We are planning to apply TLS restraints.
I do not interpret your comments as criticism. I know shortcomings but
it was a temporary solution. Like many temporary solution it turned out
to be
almost permanent.
We are preparing a version (one after the imminent release) that should
remove some of the shortcomings of current parameterisation fTLS.
Garib
On 19 May 2006, at 18:27, George M. Sheldrick wrote:
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There is another good reason why you should run TLSANL to produce the
PDB file for deposition after doing a TLS refinement in REFMAC: the
ANISOU cards it produces should in principle be unique for a given
structure, but the TLS matrices and additive isotropic B's are not!
You can add a constant value to these B values for all atoms in the
same TLS group and subtract it from the diagonal elements of the T
tensor for that group, and the fit is unchanged. In other words REFMAC
refines one parameter too many per TLS group, and if it were able to
do a full matrix refinement this would cause it to blow up with a
singular matrix (Garib: please do not interpret this as a criticism,
the REFMAC approach is a good practical solution to a tricky problem
and we make good use of the TLS refinement in REFMAC).
Possibly some future version of a refinement program will apply TLS
restraints rather than constraints, this could be programmed in a way
that would refine the Uij values directly and so avoid this problem.
The deposition of restrained Uij values would then be on a par with
the deposition of restrained atom coordinates (which we do all the
time).
George
--
Prof. George M. Sheldrick FRS
Dept. Structural Chemistry,
University of Goettingen,
Tammannstr. 4,
D37077 Goettingen, Germany
Tel. +49-551-39-3021 or -3068
Fax. +49-551-39-2582
