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Rami
rami.gherib@mail.utoronto.ca

>there is a mistake in your input file.

>You input directs Firefly to freeze torsion 3-4-14-17.

>If you look at this torsion, as can be found from the output file
>you provided, it stays constant during geometry optimization i.e.
>it is indeed frozen.

>As far as I understand, you intention was to freeze torsion 4-3-14-17
>instead. This is absolutely not the same as the torsion 3-4-14-17!
>The order of atoms is important here. You need to specify

>

 IFZMAT(1)=3,4,3,14,17

>in your input file.

>Hope this helps.

>Kind regards,
>Alex Granovsky

>
>
>
>
>On Fri May 18 '18 10:17pm, Rami wrote
>-------------------------------------
>>On Fri May 18 '18 10:15pm, Rami wrote
>>-------------------------------------
>>>Hello,

>>>I am trying to perform a geometry optimization while constraining one of the torsional angles in my molecular system. I'm using state-averaged CASSCF and I would like to optimize on the ground state potential energy surface. The problem I am facing is that during the optimization, the torsional angle that is intended to be fixed, changes significantly (from 110 to 128.6 degrees). I using the following commands to fix the desired torsional angle:

>>> nzvar=1 ! in  $CONTRL

>>>and

>>> $ZMAT DLC=.T. AUTO=.T. nonvdw(1)=1,26
>>> IFZMAT(1)=3,3,4,14,17
>>> $end

>>>I would also like to mention that I used the same set of commands to optimize the same molecule at a different fixed angle on the excited state surface. The latter did not have this problem. The input and output files are attached.

>>>Thank you,

>>>Rami
>>>