Subject: rotate molecules along princliple moments of inertia

From: "lala podibaer" <[email-masked]>
Date: Tue, 22 Oct 2002 08:38:03 +0000

Hi all,

I have a problem concerning the alignment of molecules along their principle 
moments of inertia. I read through several papers and use now a singular 
value decomposition for the alignment. At first glance everything seems to 
be ok with the rotated molecules, they are nicely aligned along the axes and 
insensitive to rotation. Unfotunately, at closer inspection of the aligned 
molecules it can be found that some of the molecules are rather mirrored 
than rotated along the principle axes.

I think the problem lies within the sorting routine of the eigenvalues. 
Since the eigenvectors are not sorted according to the largest value in the 
xyz coordinates, multiplication of the original X matrix with the 
eigenvectors doesn't necessarily produce rotated but mirrored molecules.

I am pretty certain that this problem has already been solved, but I was not 
able to find any documentation in terms of formulas which I could use for 
implementation.

I would appreciate every reference or subroutine that might help me with 
this.

Cheers
Mike

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