Hi,
After obtaining a transition state (TS) from an FSM calculation in Q-Chem 6.4, I proceeded to run an IRC calculation to connect the two ends of the reaction pathway.
While the IRC does proceed, I am encountering an issue where the trajectory appears to get stuck near the TS region. It does not smoothly propagate away toward the reactant and product minima as expected.
I used the following input:
$molecule
0 1
C -1.3584668423 0.4909721018 0.0005096194
H -1.7661285679 1.4818306420 -0.2041847896
H -1.6922307384 0.1172297313 0.9717143176
H -1.6467427918 -0.2031601338 -0.7897262709
O 0.0620917673 0.6879653187 0.0203866595
C 0.7353311179 -0.5787327527 0.5556515705
N 0.9826508724 -0.7585598344 -0.6160347207
$end
$rem
JOBTYPE ts
method wb97x-v
BASIS aug-cc-pVTZ
scf_max_cycles 600
geom_opt_max_cycles 600
scf_algorithm robust
INTEGRAL_SYMMETRY false
XC_GRID 3
POINT_GROUP_SYMMETRY false
MEM_TOTAL 80000
$end
@@@
$molecule
read
$end
$rem
JOBTYPE frequency
method wb97x-v
BASIS aug-cc-pVTZ
scf_max_cycles 600
scf_algorithm robust
INTEGRAL_SYMMETRY false
XC_GRID 3
POINT_GROUP_SYMMETRY false
MEM_TOTAL 80000
$end
@@@
$molecule
read
$end
$rem
JOBTYPE rpath
BASIS aug-cc-pVTZ
METHOD wb97x-v
SCF_GUESS read
RPATH_MAX_CYCLES 60
RPATH_MAX_STEPSIZE 300
XC_GRID 3
GEOM_OPT_HESSIAN READ
MEM_TOTAL 80000
$end
Output file:
============================================
FORWARD RXN PATH (direction = +1)
============================================
7
IRC step # 1, E = -207.812070
C -1.361313 -0.191027 0.185180
H -2.192082 -0.077267 -0.512539
H -1.530787 0.381234 1.100665
H -1.212534 -1.245259 0.421614
O -0.231333 0.343934 -0.517737
C 0.941615 0.488909 0.455588
N 1.329179 -0.513923 -0.101779
7
IRC step # 2, E = -207.812070
C -1.361311 -0.191022 0.185180
H -2.192086 -0.077268 -0.512539
H -1.530788 0.381232 1.100668
H -1.212536 -1.245256 0.421613
O -0.231334 0.343934 -0.517728
C 0.941616 0.488911 0.455573
N 1.329186 -0.513931 -0.101775
7
IRC step # 3, E = -207.812070
C -1.361305 -0.191006 0.185177
H -2.192100 -0.077271 -0.512537
H -1.530787 0.381220 1.100681
H -1.212552 -1.245242 0.421607
O -0.231328 0.343913 -0.517719
C 0.941623 0.488927 0.455556
N 1.329195 -0.513941 -0.101773
============================================
BACKWARD RXN PATH (direction = -1)
============================================
7
IRC step # -1, E = -207.812070
C -1.361313 -0.191027 0.185180
H -2.192082 -0.077267 -0.512539
H -1.530787 0.381234 1.100665
H -1.212534 -1.245259 0.421614
O -0.231333 0.343934 -0.517737
C 0.941615 0.488909 0.455588
N 1.329179 -0.513923 -0.101779
7
IRC step # -2, E = -207.812070
C -1.361310 -0.191021 0.185179
H -2.192087 -0.077269 -0.512539
H -1.530787 0.381231 1.100668
H -1.212538 -1.245255 0.421613
O -0.231332 0.343929 -0.517730
C 0.941618 0.488910 0.455577
N 1.329182 -0.513926 -0.101776
7
IRC step # -3, E = -207.812070
C -1.361307 -0.191013 0.185177
H -2.192094 -0.077270 -0.512538
H -1.530786 0.381225 1.100675
H -1.212546 -1.245248 0.421609
O -0.231328 0.343918 -0.517725
C 0.941620 0.488923 0.455570
N 1.329187 -0.513935 -0.101777
============================================
Total job time: 1426.85s(wall), 16658.43s(cpu)
Sun Mar 29 13:24:39 2026
Any suggestions on how to resolve this issue would be greatly appreciated.