Hi all, I am trying to run the MD simulation on Ag2O of cuprite structure, with a 2 by 2 by 2 supercell. I find it cannot converge. I just started to do MD on QE, so I cannot figure out what is going on. Your help is appreciated very much.
The scf calculation gives a good convergence, including the phonon frequencies calculated by PH., I also run the vc-relax, it converged too and gives an optimized lattice parameter very close to experimental data. Then I used those parameters running MD, cp.x, however, even in the first relaxation step with the constant volume, it is hard to converge. And only if ortho_max is set to 1000, the orthonormalization cannot be fulfilled. After the job is done, I find the final total stress exceeds 200 GPa. Then I restart, with a random atom displacement, it does not help. I then run the vc-cp, the cell keeps going larger, like blowing up. The temperature cannot converge as well, and far from the target. I think it is not surprising, since the initial stress in NVE is so high. I also changed the cell back to the primitive one. It performs in the same way, so I think the supercell is not the problem. I am very confused about what is happening. It appears to be a contradiction, I expected a good structure from scf calculation should more or less agree with the MD run. The basic setup is like this: I used ultrasoft potential Ag.pbe-d-rrkjus.UPF and O.pbe-rrkjus.UPF. I followed most of default settings, except, emass=700, and the emass_cutoff=3, nr1b=10, ecutwfc=30 (tried 20 to 70). The # of valence electrons are, 11 for Ag and 6 for O. If you have experience about it, please give me a hint. I can provide more information if needed. Best, Tian -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20120912/e0bf000f/attachment-0001.htm
