I am doing DFT calculations (VASP) to calculate correct binding energy for an amorphous silica surface and silver adatoms. From MD simulation, we found that a binding energy of 0.2 eV gives results which can be matched to experimental ones.
Since this is an amorphous surface, how do I go along to measure the correct binding energy. I have tried 18 runs where I have relaxed the adatom at different positions and at different heights but how many runs to do this as each result has a different value?