### Author Topic: itrvec and symmetry  (Read 6617 times)

#### cneiss

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##### itrvec and symmetry
« on: October 21, 2011, 02:38:39 PM »
Dear all,

I'm just wondering about the itrvec option if one performes the TS search using symmetry (e.g. C3v).

Example: I have the following frequencies:
...
7        e             114.55         6.42669       YES     YES
8        e             114.55         6.42669       YES     YES
9        a1            291.59        82.78354       YES     YES

I want to follow the a1-mode (the e-modes would break symmetry).

Do I have to specify itrvec=3 *or* itrvec=1, if I perform the optimization using C3v-symmetry?

Best wishes

#### Arnim

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##### Re: itrvec and symmetry
« Reply #1 on: October 24, 2011, 02:16:14 PM »
Hi,

in that example neither 3 nor 1, but itrvec=9 !?
The dimension of the Hessian is not reduced by degenerated modes. Just select the # of the mode, that you want to follow.

Best,

Arnim

#### cneiss

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##### Re: itrvec and symmetry
« Reply #2 on: October 25, 2011, 12:44:58 PM »
Hi Arnim,

the first six frequencies are zero and correspond to the translational and rotational modes.
According to the documentation, these should not be counted, or am I wrong here?

Furthermore, I was just wondering, what TM is actually doing, when I select for example an e-mode as transition vector while performing the transition state search in C3v symmetry.
The problem is, that one cannot follow the e-mode without destroying the C3v symmetry. So, what is TM actually doing in this case? Can you comment on that?
(In my simple example, it seems to me that statpt follows the lowest total-symmetric mode for itrvec=1.)

Best,
Christian

#### Arnim

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##### Re: itrvec and symmetry
« Reply #3 on: October 25, 2011, 01:22:40 PM »
You are right. The first six zero are not counted. I didn't read it carefully.