Step 1. Prepare molecule

First create a TlH (thallium hydride) molecule with a bond length of 1.87 Angstrom (the experimental bond length):

Open ADFinput and draw a TlH molecule.
Select the Tl and H atoms
Set the distance between the atoms 1.87 Angstrom (use the distance input field below the molecule)

Select Symmetry → Clin (the symmetry menu pops up if one clicks the five-pointed star button)
Select Symmetry → Set C axes
Next Select Symmetry → Symmetrize
Select Model → Coordinates

The coordinates should like like:

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