Relax PES scan in Q chem

I am running relax PES scan of passing proton through the center of Benzene from 2.2 Angstrom to -0.8 Angstrom. I have Dummy atom placed at a -0.8 Angstrom along the Z axis. I am receiving the following error. Can any give me an idea how to solve this. The input and error is given below
$molecule
1 1
C 1.22127000 0.70510000 0.00000000
C 1.22127000 -0.70510000 0.00000000
C 0.00000000 1.41021000 0.00000000
C -1.22127000 -0.70510000 -0.00000000
C -0.00000000 -1.41021000 -0.00000000
C -1.22127000 0.70510000 -0.00000000
H 2.15657900 1.24509729 0.00000000
H 2.15657900 -1.24509729 0.00000000
H 0.00000000 2.49021000 0.00000000
H -2.15657900 -1.24509729 -0.00000000
H -0.00000000 -2.49021000 -0.00000000
H -2.15657900 1.24509729 -0.00000000
H 0 0 2.2
X 0 0 -0.8
$end

$FIXED
14 0 0 -0.8
$ENDFXIED

$rem
BASIS = def2-TZVP
JOBTYPE = PES_SCAN
MAX_SCF_CYCLES = 100
METHOD = B3LYP
SCF_ALGORITHM = GDM
SCF_CONVERGENCE = 5
THRESH = 14
$end

$scan
stre 13 14 -0.8 2.2 0.1
$end
Error: ERROR Distance Constraint must be positive

Q-Chem fatal error occurred in module 0, line 9:

OPTIMIZE fatal error

I think it’s telling you that the “stre” type is a bond length, not an absolute coordinate, so it cannot be negative.

So what could be the possible solution?

What Prof. Herbert is suggesting is “-0.8” in your $scan cannot be a negative number, because a bond length cannot be negative.

Examples here:
https://manual.q-chem.com/6.2/Ch9.S6.SS1.html

Thanks for your reply. I do know how to do PES_SCAN. But since my proton has to pass through the center of the benzene ring from +Z direction towards - Z direction, for that I have to define Dummy atom which makes it complicated. I am constantly getting error that Dummy atom has to be part of the constraint which it is already. If you know how to deal with that, please let me know. Thanks
$molecule
1 1
C 1.22127000 0.70510000 0.00000000
C 1.22127000 -0.70510000 0.00000000
C 0.00000000 1.41021000 0.00000000
C -1.22127000 -0.70510000 -0.00000000
C -0.00000000 -1.41021000 -0.00000000
C -1.22127000 0.70510000 -0.00000000
H 2.15657900 1.24509729 0.00000000
H 2.15657900 -1.24509729 0.00000000
H 0.00000000 2.49021000 0.00000000
H -2.15657900 -1.24509729 -0.00000000
H -0.00000000 -2.49021000 -0.00000000
H -2.15657900 1.24509729 -0.00000000
H 0 0 2.2
$end

$dummy
14 2 3 13
$enddummy

$rem
BASIS = def2-TZVP
JOBTYPE = PES_SCAN
MAX_SCF_CYCLES = 100
METHOD = B3LYP
SCF_ALGORITHM = GDM
$end
$scan
stre 13 14 0.0 3.0 0.1

If you’re trying to put a proton atop benzene, why not just do it on one side and then flip everything by symmetry?

By this do you mean that I should remove the dummy atom and scan it just from one side? If yes then How I will let the proton go through the center of the benzene ring?

It has C6v symmetry, it’s the same on both sides. More to the point, you can probably do this even without constraints, due to the symmetry. GEOM_OPT_DRIVER = OPTIMIZE is better at preserving the initial point-group symmetry.

OK thank you very much for the suggestions.