Author Topic: problems with statpt in TS search  (Read 6971 times)

lasermichel

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problems with statpt in TS search
« on: August 31, 2007, 12:23:32 pm »
Dear all,

We have a problem using stapt for determining the (a) transition state of the azaindole-water cluster. After running statpt the first time we have 4 negative eigenvalues in the stapt output. Running aoforce at the unchanged geometry shows only positive frequencies or sometimes a different number of negative frequencies at the same level of theory. If we start at this (unchanged) geometry a new optimization using jobex -trans, we often end up in a minimum along all modes.
The same thing happens, if we elongate along one of the modes with negative frequency using the screwer tool.

Maybe this is due to the fact, that during optimization we cannot change the step size for the search algorithm. So we might just "pass" over the TS? Is there any way to adapt another step size especially concerning TS search?

Thanks so lot

Michael   

turbomaster

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Re: problems with statpt in TS search
« Reply #1 on: September 21, 2007, 11:23:13 pm »
Hello

Vacation is over so its time to answer some questions  ;D
You probably used a Hessian update method within statpt. This results in only an approximate
Hessian matrix which can well have several negative eigenvalues, which most probably
will not be the same as calculated with analytical (aoforce) Hessian.
Did you calculate Hessian with aoforce prior to running TS optimization? If nothing helps
you can try to run statpt with analytical Hessian calculated every 3-5 steps. This will be
expensive but should lead finally to TS.
The step size in statpt is adjusted automatically. You can only specify initial and maximum
step size (using define menu). Try to decrease the maximum step length, it may also help.
« Last Edit: May 12, 2008, 10:37:46 pm by turbomaster »