Hi all
I am studying a cationic cluster containing one molecule of methanol and one molecule of halobenzene, I am investigating a possible intra-cluster reaction leading to the formation of anisole, First I did QST3 calculations and got a reasonable transition state structure (with one imaginary frequency), as I do IRC calculations to verify that I get valid reactants and products structure however the total energy along IRC plot gives me a flat line (basically no energy difference throughout the path). does anyone know what does that mean? does it mean the transition state I found is not valid?
appreciate any help on this
Hello,
You can check the vectors of the imaginary frequency to see where they lead.
Is the magnitude of your imaginary frequency large? If so, then maybe you could try adding IRC=recorrect=never and also increasing the number of points to be computed.
Regards,
Dilawar
Dilawar Singh Sisodiya Thanks for your reply , yes the imaginary frequency is pretty high (~-3900) I have tried turning off the re-correction but still getting the same issue,
how can I check the imaginary frequency vectors?
@Tahereh Alavi You can use GaussView or any other software to visualize them. In GV you can check the box with "Show Displacement Vectors".
Are you calculating Hessian for the IRC run or reading it from previous run?.
Is it possible that your reaction has flat PES?
Dear Dilawar Singh Sisodiya Thanks for your answer. yes I calculate force constants. I checked the displacement vector for the imaginary frequency and looks fine. the IRC results in structures leading to the expected reactants and products so I think the transition state is valid, However the molecule group table looks strange! the energy of the first structure (reactants) looks right but all other structures have extremely lower energy (I have a feeling that it is calculating their relative or difference energy for some reasons, I have attached the screenshot showing the table). Would you please take a look at the input file.
# irc=(calcall,recorrect=never,maxpoints=80) ub3lyp/3-21g maxdisk=9GB
formcheck
Title Card Required
1 2
C -0.28311989 -0.20536304 0.11648284
C 0.25303767 1.04754813 0.58125522
C 0.54513511 -1.13190188 -0.61116896
C 1.59522255 1.28616211 0.43215802
H -0.39689325 1.74444016 1.09397357
O -1.73111934 -0.26882460 -0.25674273
F -0.88776597 -1.02697992 1.51451290
C 1.88412105 -0.86455629 -0.74454851
H 0.08420530 -2.02547256 -1.00998815
C 2.42778905 0.33749642 -0.22268825
H 2.02772129 2.20218339 0.81370368
C -2.44658717 0.86186492 -0.94348093
H -1.90735135 -0.75963396 0.77924012
H 2.52786518 -1.56270950 -1.26371397
H 3.48571144 0.54031505 -0.33145373
H -1.94686086 1.01919580 -1.89791218
H -2.42874800 1.75519409 -0.31952071
H -3.46039155 0.49240137 -1.08905938
Dear Tahereh Alavi, I use #p, which gives me more detailed output.
At the end of the IRC run, you should find a summary table for IRC (see below). Energies are reported relative to the TS. In the table below, you can see that the 'RxCoord' is 0 (TS) for step 31, for which energy is also 0. Energies are reported in Hartree.
Energies reported relative to the TS energy of -2748.264404
--------------------------------------------------------------------------
Summary of reaction path following
--------------------------------------------------------------------------
Energy RxCoord
1 -0.02685 -9.03293
2 -0.02680 -8.73091
3 -0.02675 -8.42814
4 -0.02668 -8.12506
5 -0.02660 -7.82190
6 -0.02650 -7.51867
7 -0.02639 -7.21556
8 -0.02627 -6.91254
9 -0.02612 -6.60973
10 -0.02596 -6.30878
11 -0.02580 -6.01056
12 -0.02559 -5.71187
13 -0.02535 -5.41221
14 -0.02509 -5.11107
15 -0.02480 -4.81627
16 -0.02453 -4.52203
17 -0.02413 -4.22133
18 -0.02369 -3.91985
19 -0.02317 -3.61860
20 -0.02254 -3.32205
21 -0.02192 -3.03135
22 -0.02061 -2.73539
23 -0.01872 -2.43205
24 -0.01625 -2.12816
25 -0.01340 -1.82413
26 -0.01038 -1.52009
27 -0.00739 -1.21605
28 -0.00462 -0.91202
29 -0.00228 -0.60801
30 -0.00062 -0.30406
31 0.00000 0.00000
32 -0.00068 0.30411
33 -0.00275 0.60812
34 -0.00600 0.91215
35 -0.01007 1.21618
36 -0.01464 1.52024
37 -0.01945 1.82429
38 -0.02426 2.12834
39 -0.02882 2.43235
40 -0.03283 2.73620
41 -0.03604 3.03950
42 -0.03845 3.34188
43 -0.04030 3.63949
44 -0.04145 3.92916
45 -0.04256 4.22821
46 -0.04342 4.52884
47 -0.04410 4.82859
48 -0.04458 5.12804
49 -0.04501 5.42841
50 -0.04537 5.72598
51 -0.04563 6.01709
52 -0.04573 6.12915
--------------------------------------------------------------------------
Tahereh Alavi, If you have made your table relative to the reactant energy then the energy of reactant should be zero.
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