Question

Calculation correct binding energy for a system?

Answer 1

What, precisely, do you want to know? For an amorphous surface one would expect a range of binding energies because each surface 'site' is a little different from the others. So, you are looking at a spread of binding energies and you would need to characterize the shape of that spread. Now, you will also have to consider the possible errors and variation in DFT itself, which can be considerable depending on the system.