Step 1. Prepare molecule

Open ADFinput and draw a TlH molecule.
Select the Tl and H bond and make the length 1.87 Angstrom
  (= experimental bond length).
You can change the length, for example, by changing the value
  in the box below the drawing area.

Select 'Clin' from the 'Symmetry' Menu (the button which initially shows 'Nosym'
     on the top of the drawing area).
Select 'Select All' from the 'Edit' Menu.
Select 'Set C axes' from the 'Symmetry Menu'.
Next Select 'Symmetrize' from the Symmetry Menu'.
Select 'Coordinates' from the 'Model' Menu, which now should look like:

Note that the molecule is now in the standard C_∞v (CLIN) orientation, which ADF will use in the calculation.