IRC calculation out file

Questions
#1

I was tried to IRC calculation , where i got path calculation in out file after completed job.

#2

This is admittedly confusing and the output is not reported in a nice way. (There is some internal discussion that this needs to be cleaned up but it hasn’t happened yet.) Let me walk you through this, using the sample job rPath_HCN.in whose input is the following:

$molecule
0 1
 C 
 H  1 1.201911
 N  1 1.221378 2 72.763366
$end

$rem
jobtype freq
basis sto-3g
method hf
$end


@@@
$molecule
0 1
 C 
 H  1 1.201911
 N  1 1.221378 2 72.763366
$end

$rem
RPATH_MAX_CYCLES 30
jobtype rpath
basis sto-3g
scf_guess read
method hf
rpath_direction -1
gui 2
$end

The second job is the IRC search (JOBTYPE = RPATH), so please go to that part of the output. There you will find a line that says

In first_irc_step: ISign =           -1

This is the start of a backwards IRC search (reverse direction, -1). The converged steps along that path are labeled with blocks of text that look like the following (corresponding to the first step):

 ------------------------------------------------------------------------
 Reaction path following.  The coordinates are cartesian
 Step   1 E=     -91.564851 |G|=  0.000107 S_lin= 0.0000 S_tot= 0.0000
 ------------------------------------------------------------------------

This particular path consists of 26 steps, the final one is labeled with:

 ------------------------------------------------------------------------
 Reaction path following.  The coordinates are cartesian
 Step  26 E=     -91.644430 |G|=  0.002219 S_lin= 2.2827 S_tot= 2.4468
 ------------------------------------------------------------------------
  IRC -- convergence criterion reached.

Then a few lines later the search begins for the forward path:

 Starting direction for rxn path = 1

which consists of 18 steps, terminating with:

 ------------------------------------------------------------------------
 Reaction path following.  The coordinates are cartesian
 Step  18 E=     -91.675183 |G|=  0.003630 S_lin= 1.8185 S_tot= 1.8906
 ------------------------------------------------------------------------
  IRC -- convergence criterion reached.

Importantly, there are more than 18 + 26 separate geometries in the output (143 separate geometries in this case), because multiple energy + gradient calculations are required to locate each point along the IRC. Therefore you need to be careful about which geometries that you extract. (This could be done much better on Q-Chem’s end and I will update the bug ticket / discussion to emphasize that fact.) Meanwhile what can you do, given the present state of the code? You will need to use some simple to extract the geometries that you want. Whenever you see a converged step (“Reaction path following…” messages above), the coordinates that you want are actually the set of coordinates printed prior to that message, not the set of coordinates that appears just below the message, which corresponds to the beginning of the calculation for the next step.

Update: I have looked into the code, and I will implement a better output for Q-Chem 6.0.2 release.

#3

For future reference, for v. 6.0.2 the output has been cleaned up and put in readable form at the end of the Q-Chem output, no scripting required.