Subject: A. Turner/Delocalized Coords

From: [email-masked] (Folke Noertemann)
Date: Tue, 21 Apr 1998 13:54:39 +0200

Dear Alex Turner,
 I received your mail a few minutes ago, but
by some unfortunate accident the 'delete'-button
was hit (honestly -this never happened to me before!)
and thus I cannot reply directly to you.

The procedure you mention is most easily applied
to Z-Matrix coordinates or any other set where you
have direct control over the actual dihedral angles
themselves. With delocalized coordinates the situation
is somewhat more complicated since they are linear
combinations of stretches, angles and dihedral angles.
However, it is obviously not impossible to readjust
the jumps in the coordinates underlying the linear
combinations. My attention was drawn to this by Cory C. Pye,
who also replied directly to me last night.
As you also say, it requires some amount of book-keeping in the 
backtransformation from internal to cartesian coordinates and
probably out of a certain inertia I didn't realize
that I don't have to put up with the restriction of avoiding
180 dihedrals.

This in turn would simplify my actual problem to a large extent.
(generating dummy atoms such that a 180-dihedral is
avoided and still having a complete description of 
the coordinate space).

I would be glad if you still had a backup of the e-mail you sent
me. Could you forward it to me again? 
Thanks a lot ,
  Folke

F. Noertemann
Lehrstuhl f. Theoret. Chemie
TU Muenchen
[email-masked]