Step 6: Following the reaction coordinate

ADF can follow the minimum-energy path from the transition state to one or the other product. The method used in ADF for this is called Intrinsic Reaction Coordinate (IRC). This tutorial step is optional because it might take some time to complete.

Bring HCN_Freq2 in ADFinput to the front
Select the "IRC" preset
Go to the 'Task: IRC panel'

The 'Task: IRC' panel, on the right-hand side, allows you to specify various parameters for the IRC method. The most important parameter is the direction to follow. The choice is more or less arbitrary. By choosing "Forward path" or "Backward path" will lead you to one or the other product but it's hard to tell which of the two in what case. We will calculate both paths at once, thus we do not need to change the default.

Type 'HCN_IRC' in the 'Title:' field of the 'Main Options' panel 
Save as HCN_IRC
Run

After some minutes the calculation will finish. You can use ADFmovie to view the IRC path. Of course you need again to make sure to show the converged geometries only:

Select the SCM → Movie command
Select the View → Converged Geometries Only command

From this movie you can see the IRC path, and the energies at the most interesting points. As we have calculated the forward and backward path in one run, in the movie you will first see the IRC in one direction (forward), and next resuming in the other direction (backward).

You can also examine some properties along the IRC path by studying the output file:

Select SCM → Output
Use the Other Properties → IRC Path menu command

You will see a table with the properties along the forward path. To get the backwards path:

Click on the blue header 'Dist from TS ...'

The output browser should jump to the next section with that header, which is the table for the backward IRC path.