# CCL:G: Cartesian Coordinate Transformation

*From*: Sigismondo Boschi <s.boschi()cineca.it>
*Subject*: CCL:G: Cartesian Coordinate Transformation
*Date*: Wed, 3 May 2006 09:35:55 +0200 (MEST)

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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