Dear Wien2k mailing list, I've been doing some calculation on a moderately large (around 100 atoms) amorphous-like SixTi1-xO2 cells produced by simulated annealing MD in a PAW software. According to my colleague who did the final force relaxation, the residual forces on atoms should be around 0.5 mRyd/Bohr. However when I calculate forces in Wien2k I see forces of order of magnitude larger, eg. some as large as 30mRyd/Bohr.

This are exactly the same calculations: both using PBE, same k-grid, same RKMAX (calculated from cutoff using the formula from UG) and I've spent a lot of time checking the force convergence with respect to all possible parameters. We did some tests with small cells (eg. 10 atoms) and there we can get a consistent results with max difference of forces around 10-20% which I find reasonable. I'm actually quite clueless about it. I've been suspecting user error at the beginning however I haven't found any so far. My current theory is that in this large cases without symmetry maybe the small differences between methods somehow sum up and hence the big difference in final forces, however I would like to hear your opinion in this matter. Best regards Pavel Ondračka _______________________________________________ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html