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2+2 transition state search

Jonas Baltrusaitis
jonas-baltrusaitis@uiowa.edu

I have these two wonderful molecule before and after reaction and the reaction is 2+2 internal reorganization. I would like to calculate transition state but to all fairness I fail due to several facts:
-it's 2+2 organization so there is 4 total atoms involved. whenever I calculate initial guess Hessian (with some other software) it always gives 2 negative frequencies, one for symmetric one for antisymmetric stretch of those 4 atoms. That might mean that there is 2 TS where 2 atoms react...

But I digress... Briefly, in FF I can't get decent initial guess. If I take constrained optimization between initial and final structures, calculate Hessian and start TS search, structure clearly goes the wrong way.

How do I obtain good initial guess for this TS? In Gaussian there is several TS methods where one input initial and final coords. Is there such a thing in FF?

Any other comments?

thanks

Jonas

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