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Dear Phil,
thanks for your answers!
Phil Jeffrey wrote:
...
3. On the one hand I think it would help, since you account for a large
proportion if intra-molecular (self) vectors, although obviously not the
inter-molecular (cross) vectors. On the other hand, what you're
essentially doing is symmetrizing the probe Patterson from P1 to the
point group of the target (unknown) at each rotation point, and since
the unknown already has that symmetry it may yet prove to be mostly
redundant since the rotation function is a product function. In the
back of my mind I'm wondering if it is equivalent to averaging the
product of the two Pattersons about the crystallographic symmetry, at
any given trial rotation, which is already done by virtue of the
symmetry of the unknown.
...
It this point that I had in my mind. I would like to account
simultaneously for_all_ symmetry-equivalent intra-molecular Patterson
vectors at once. Since the intra-molecular Patterson vectors of all
symmetry copies of the true structure fall into the same sphere around
the origin, any true orientation of the search molecule will have its P1
Patterson self-vectors overlapping both with the self-vectors of the
corresponding true molecule, which will add to the signal, _and_ with
the self-vectors from its symmetry copies, which will add to the noise.
Fitting them all simultaneously by applying the rotational symmetry of
the space group to the P1 self-vectors of the search molecule would
result in a Patterson overlap with all self-vectors of the true
structure at once. This should enhance the signal-to-noise ratio of the
orientation search.
What do you and others think about this?
Best regards,
Dirk.
--
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Dirk Kostrewa
Paul Scherrer Institut
Biomolecular Research, OFLC/110
CH-5232 Villigen PSI, Switzerland
Phone: +41-56-310-4722
Fax: +41-56-310-5288
E-mail: [EMAIL PROTECTED]
http://sb.web.psi.ch
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