Problem Finding Transition State H2CO3

I am currently trying to calculate the transition state of the reaction H2CO3 -> H2O + CO2. But I only get either the reactant or the products, depending on the starting structure.
I tried it with different starting structures and also with the transition state structure itself, but I always got either the H2CO3 structure or H2O + CO2. Does anyone have an idea how to fix this?

My Input File:

# H2CO3

memory 4000 MB

molecule {
C -0.0110 0.0053 0.0002
O -0.1653 1.4249 -0.0075
H 0.7565 1.6928 -0.0007
O -1.4306 -0.1491 -0.0135
H -1.5926 1.3421 -0.0216
O 1.0890 -0.5317 0.0123

set {
basis cc-pVDZ
dynamic_level 1
g_convergence gau
print_trajectory_xyz_file True
opt_type ts


If you check your output file, you might be able to see if the force constants you are computing with ‘frequency’ are actually being used by the optimizer (as opposed to an empirical one). I suspect not. The admittedly not very intuitive way to accomplish what you are doing is with

full_hess_every = 0

which will compute the Hessian (and transform and use it) once at the beginning of the optimization.

full_hess_every = 1

computes the hessian at every single step. If you use this keyword, you do not need the first, explicit frequency call. It is impied.

Beyond that, you are right to try different starting geometries, as the better your first guess, the more likely you are to converge.

That did the trick, thank you very much.