Hi Q-Chem developers!

I’m currently running multiple harmonic frequency calculations but I have found a problem with one particular molecule not converging properly (COClF - smiles code: C(=O)(F)Cl). Both the displacement and energy change converge to the desired value. However, the gradient gets close to converge but it doesn’t after all optimisation cycles; it basically stays in the same value pretty much through all the calculation (hope the data below helps visualise this):

```
Gradient 0.000064 0.000015 NO
Displacement 0.000006 0.000060 YES
Energy change -0.000000 0.000001 YES
```

I’ve tried multiple things including using different basis sets, turning the symmetry off, and using alternative initial geometries (including a Z-matrix representation), but it just doesn’t work. I’m wondering if you guys could help with it? (it might not be a problem related with the program, but maybe there’s a keyword that I’m missing). Here’s a copy of the input file:

$comment

QCHEM - COClF

Geometry optimisation and vibrational frequencies

$end

$molecule

0 1

C 0.4911656443 0.1216536157 -0.0000048240

O 1.1314045225 1.1042136062 0.0000015411

F 1.0009499982 -1.1013888005 0.0000010333

Cl -1.2356929429 0.0205216859 0.0000004304

$end

$rem

JOBTYPE OPT

SYMMETRY FALSE

METHOD TPSS0

BASIS AUG-cc-pVTZ

SCF_CONVERGENCE 8

GEOM_OPT_MAX_CYCLES 100

GEOM_OPT_TOL_GRADIENT 15

GEOM_OPT_TOL_DISPLACEMENT 60

XC_GRID 3

$end

@@@

$molecule

READ

$end

$rem

JOBTYPE FREQ

SYMMETRY FALSE

METHOD TPSS0

BASIS AUG-cc-pVTZ

SCF_CONVERGENCE 8

XC_GRID 3

$end

Cheers,

Juan