I use Siesta-2.0.2. I need to calculate surface formation energy very precise. But these fluctuations produce errors well below 0.1 meV/Ang2 so I am satisfied. I will try to increase cutoff and follow how the numerical noise change, just for curiosity. >From the graph I posted the calculation is converged at 30 Ang (15 Ang vacuum space), isn't it?
Ruslan 2010/4/18 Marcos Veríssimo Alves <[email protected]> > Ruslan, > > This is already off the limits of DFT precision... I'd say it's just > numerical noise. If the fluctuations were much larger (say, of the order of > a few tens of eV), then I might be tempted to wonder about it. I would say > your calculation is already very well converged at about 70-80 Angstrom. By > email correspondence, a friend told me that this convergence problem could > be greatly diminished by increasing the mesh cutoff, which really leads me > to think this could be a spurious numerical issue, maybe a spurious dipole > moment. Try doubling the mesh cutoff, or even multiplying it by three, and > check out what the effect is on the numerical results. However, if you're > using siesta 3.0, have you tested the feature of dipole correction for > slabs? (This is actually a question driven by curiosity, since I have not > tested it myself but would love to know what its behavior is like) It could > save you some cutoff increase - wild guess. > > Cheers, > > Marcos > >
