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Re^2: freezing bond length in IRC job

Alex Granovsky

Hi Jim,

well, there are lots of people (including myself) who believes
that INTRINSIC REACTION COORDINATE does not have much sense at
all - e.g., unlike stationary points on PES, it is non-invariant
with respect to arbitrary diffeomorphic transformation of
coordinate system. More precisely, if you calculate IRC, then
transform coordinates, calculate IRC in new coordinates, and then
back-transform coordinates, the two IRCs will be different.


On Mon Jun 21 '10 6:37pm, Jim Kress wrote
>Doesn't "freezing" a coordinate in an INTRINSIC REACTION COORDINATE calculation defeat the whole purpose of performing the INTRINSIC REACTION COORDINATE calculation?  After all, you are looking for a reaction path which, if you "freeze" one coordinate, will not be a reaction path, it will be just an artificial construct that has no real physical meaning.

>Look here:


>for some deeper insight.

>On Sun Jun 20 '10 9:29pm, Eldar Mamin wrote
>>Dear Fireflly Users,

>>Can I freez bond length in IRC job?

>>To define molecule I use Z-matrix, and function ifreez to make coordinate frozen. Following that way I get Saddle point, but during runtyp=irc  no coordinate is kept frozen.  

>>Can anyone help me?

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