Gaussian 03 Online ManualLast update: 2 October 2006 | |

## IRCThis
method keyword requests that a reaction path be followed [151,152].
The initial geometry (given in the molecule specification section) is that of
the transition state, and the path can be followed in one or both directions from
that point. By default, the The geometry
is optimized at each point along the reaction path such that the segment of the
reaction path between any two adjacent points is described by an arc of a circle,
and so that the gradients at the end points of the arc are tangent to the path.
The path can be computed in mass-weighted internals, Cartesians or internals coordinates.
By default, an IRC calculation steps 6 points in mass-weighted internals in the
forward direction and 6 points in the reverse direction, in steps of 0.1 amu IRC calculations require initial force constants to
proceed. You must provide these to the calculation in some way. The usual method
is to save the checkpoint file from the preceding frequency calculation (used
to verify that the optimized geometry to be used in the IRC calculation is in
fact a transition state), and then specify IRC calculations accept Z-matrices or Cartesian coordinates as molecule specifications and uses these coordinates in following the reaction path. You should specify alternative isotopes
for IRC studies are not currently archived. ## PATH SELECTION OPTIONS
## COORDINATE SYSTEM SELECTION OPTIONS
The force constants
are in lower triangular form: ((F(J,I),J=1,I),I=1,NAt3),
where ## OPTIMIZATION ALGORITHM-RELATED OPTION
## RESTART OPTION
HF, all DFT methods, CIS, MP2, MP3, MP4(SDQ), CID, CISD, CCD, CCSD, QCISD, CASSCF, and all semi-empirical methods. The output for each step of an IRC calculation is very similar to that from a geometry optimization. Each step is introduced by this banner line (where "IRC" has replaced "Grad"): IRC-IRC-IRC-IRC-IRC-IRC-IRC-IRC-IRC-IRC-IRC-IRC-IRC-IRC-IRC-IRC-IRC As the optimization at each point completes, the optimized structure is displayed: Optimization completed. -- Optimized point # 1 Found. ---------------------------- ! Optimized Parameters ! ! (Angstroms and Degrees) ! -------------------- -------------------- ! Name Value Derivative information (Atomic Units) ! -------------------------------------------------------------------- ! CH1 1.3448 -DE/DX = 0.0143 ! ! HH 0.8632 -DE/DX = -0.0047 ! ! CH2 1.0827 -DE/DX = 0.0008 ! ! HCH 106.207 -DE/DX = -0.0082 ! -------------------------------------------------------------------- RADIUS OF CURVATURE = 0.39205 NET REACTION COORDINATE UP TO THIS POINT = 0.09946 Once the entire IRC has completed, the program prints a table summarizing the results: -------------------------------------------------------------------- SUMMARY OF REACTION PATH FOLLOWING: (Int. Coord: Angstroms, and Degrees) -------------------------------------------------------------------- ENERGY RX.COORD CH1 HH CH2 1 -40.16837 -0.49759 1.54387 0.73360 1.08145 2 -40.16542 -0.39764 1.49968 0.74371 1.08164 3 -40.16235 -0.29820 1.45133 0.76567 1.08193 4 -40.15914 -0.19914 1.39854 0.80711 1.08232 5 -40.15640 -0.09946 1.34481 0.86318 1.08274 6 -40.15552 0.00000 1.30200 0.91500 1.08300 7 -40.15649 0.09990 1.26036 0.96924 1.08330 8 -40.15999 0.19985 1.21116 1.03788 1.08349 9 -40.16486 0.29975 1.16418 1.10833 1.08353 10 -40.16957 0.39938 1.12245 1.18068 1.08328 11 -40.17324 0.49831 1.09260 1.25158 1.08276 -------------------------------------------------------------------- TOTAL NUMBER OF GRADIENT CALCULATIONS: 28 TOTAL NUMBER OF POINTS: 10 AVERAGE NUMBER OF GRADIENT CALCULATIONS: 2.80000 The initial geometry appears in the middle of the table (in this case, as point 6). It can be identified quickly by looking for a reaction coordinate value of 0.00000. |