Help finding transition state energy (OPTKING?)

Hello again Psi4 Forums! I am currently exploring the transition state of the E2 reaction of 2br-butane with methoxide. The resulting transition-state geometry appears to be correct. However, the energy of the transition state is lower than the reactants. The energy of the product (1-butene, methanol, and bromine ion) is the lowest in overall energy… which was expected. Here is the input file I am using to calculate the transition state:

-Start-

molecule {

symmetry c1
-1 1
C -2.3101722313 0.2104912922 -0.8094616754
C -1.6219544600 1.5668282278 -0.7043956382
C -0.1927399701 1.5651137284 -1.2501884649
C 0.3696783546 2.9773198044 -1.3807000573
H -1.8058446112 -0.5519841460 -0.2089002462
H -2.3403527938 -0.1332661494 -1.8482170587
H -3.3412908180 0.2850390274 -0.4487734827
H -1.6371269559 1.8948636663 0.3424910504
H -2.2227583629 2.2901298795 -1.2693749068
H -0.1194261522 3.5408436228 -2.2024873447
H 1.4491551604 2.9571054721 -1.5819381603
H 0.2277974282 3.5441706295 -0.4518612111
Br 0.9818132082 0.5661146303 -0.0310500801
H -0.1311578154 1.0446737979 -2.2114463461
O -0.2960754191 3.7889246840 -3.1313269864
C -0.2802581345 5.1951141560 -3.3339832772
H 0.4931973543 5.6557337735 -2.7128137897
H -1.2581076724 5.6072053262 -3.0747206162
H -0.0655291090 5.3981215769 -4.3858647084

}

set {
basis cc-PVDZ
opt_type ts
geom_maxiter 200
}

frequencies(‘b3lyp’)
optimize(‘b3lyp’)

-End-

Should I be approaching this question differently? I have also tried using the opt type “irc” and computing a starting Hessian as was mentioned in the manual (http://www.psicode.org/psi4manual/master/optking.html)

Thanks!

Cam

Do you end of finding the expected transition state or something else?

I attached a picture that shows the transition state the optimizer ends at. This looks correct… but I am surprised it returns an energy level that is lower than the starting reactants. The optimizer also reports a failure to calculate the torsion angle. Does that help?

Thanks,

Cam

Oh i think i understand now. You take the reactant at infinite separation for comparison right?

Before reacting they will form an encounter complex (EC), this is a big gain in energy,
and the TS will be closer in energy to the EC than to the free reactants.
The typical approach to formulate these reactions would thus be:
reactants -> EC -> TS -> product.

Then you should get a barrier of few kcal/mol.

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