Step 3: Finding the transition state: prepare approximate Hessian

It is important to have a good starting Hessian with one imaginary frequency when performing a TS search. We are going to create such a Hessian by doing a quick frequencies calculation:

Select the "Frequencies" preset (from the 'Main' panel)
Set the integration accuracy to 4.0
Change the symmetry back to AUTO
Save the molecule with as 'HCN_Freq1' (Save As)
Run the calculation

The frequency calculation is now in progress and will run very fast. When it has finished:

Select the SCM → Spectra command

If everything was done correctly, you should see a spectrum with three peaks: two in the range of 2000 1/cm and one peak in the range of negative or very low positive values. A negative frequency value actually means that it is an imaginary frequency.

Click with your mouse on the peak corresponding to the imaginary frequency

The ADFmovie program will start displaying the normal mode corresponding to the frequency. Check that the frequency indeed corresponds to the H atom moving parallel to the C-N bond.