# Example: IRC for HCN¶

Download IRC_HCN.run

#!/bin/sh

# == IRC scan of the reaction path ==

# The IRC calculation is split in two steps to illustrate the Restart feature.

# In the first calculation only a few points are computed along the so-called
# 'forward' path. The definition of which is 'forward' and which is
# 'backward' depends on the sign of the largest component of the normal mode
# corresponding to the reaction coordinate.

# The RKF file from this partial IRC scan serves as restart file
# for the next calculations that will continue the IRC scan.

# The 'MaxPoints' key in the IRC block is used to limit the number of IRC
# points to compute.

AMS_JOBNAME=irc1 $AMSBIN/ams << eor Task IRC System Atoms C 0.000000000000 0.000000000000 0.000000000000 N 0.000000000000 0.000000000000 -1.182644220000 H -1.103250760411 0.000000000000 -0.322462130000 End End IRC MaxPoints 5 Direction Forward CoordinateType Cartesian InitialHessian Type Calculate End End Engine DFTB Model DFTB3 ResourcesDir DFTB.org/3ob-3-1 EndEngine eor # In the second IRC run, the IRC scan is finished. We start with the RKF file # from the previous run and omit the MaxPoints from the settings, which means # that the default 100 will be used. Note that the 100 also includes any points # computed in the previous calculation. The program starts on # the forward path, continuing where the first calculation had stopped, # and completes it. Since we set the Direction to Both # then AMS proceeds to the backward path. After both paths are finished a summary # of the path characteristics is printed at the end of the output file. AMS_JOBNAME=irc2$AMSBIN/ams << eor

System
Atoms
C       0.000000000000       0.000000000000       0.000000000000
N       0.000000000000       0.000000000000      -1.182644220000
H      -1.103250760411       0.000000000000      -0.322462130000
End
End

IRC
Restart
File irc1.results/ams.rkf
End
! Change options from the ones found in the restart file
! (MaxIRCPoints and MaxPoints will be reset to defaults automatically)
Direction Both
End

Engine DFTB
Model DFTB3
ResourcesDir DFTB.org/3ob-3-1
EndEngine

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