CCL:G: Cartesian Coordinate Transformation

 Sent to CCL by: Sigismondo Boschi [s.boschi()cineca.it]
 Xiaobo Zheng xiaoboccl:+:gmail.com wrote:
 
 Sent to CCL by: "Xiaobo  Zheng" [xiaoboccl#%#gmail.com]
 Dear CCLer,
 I am using Gaussian to optimized geometries with constraints and my input format
 is in cartesian coordinate.  But after optimization, somtimes, Gaussian output
 does not contain my original cartesian coordinate information.  Instead, it
 reports "standard orientation", which is a transformation of my
 original coordinate.  I am just wondering if there is an easy way or tools to
 transform Gaussian "starndard orientation" back to my cartesian
 coordinate.
 
 Hi,
I was playing with rotations just in these days... I would do it in this way: 
 - get the inertia tensor I of the original molecule
- find the corresponding rotation matrix R that rotate it in its standard orientation, by finding the eigenvalues of I. 
 - apply the inverse of R to the last molecules got from gaussian.
The two molecules now should come in a "similar" orientation... you can not state that they are in the same, since the two molecules are different. Just their inertia tensor are in the same orientation.
Otherwise, if you want to let the two molecules have a particular group aligned, like a phenyl, you need to play differently with rotations/translations. 
 I hope this helps.
 Regard,
    Sigismondo
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