Dear Stefano, Thanks for the quick reply. This was really necessary to confirm since the calculations are expensive. And I am more interested in the ground state structure, may not use the actual value of the force for further analysis.
Madhura. > In PWscf the forces are calculated from the Hellman-Feynman theorem > (strictly true only at the stationary point) plus a correction that > (approximately) accounts for the residual lack of self-consistency. As > such when the correction is large compared to the Hellman-Feynman term > one should be careful. > In your case I would say that the forces are now probably very small > and therefore the structure is reliable. > I would say that the actual (small) value for the force are probably > correct within a few percent since the correction term is (according to > the value quote) of the order of 10 % of the total (and hopefully is not > completely wrong). > Hope this helps, > stefano de Gironcoli -SISSA and DEMOCRITOS > > Madhura Marathe wrote: >> Dear all, >> >> During one of the ionic relaxation calculations, I got the error >> message, >> "SCF correction compared to forces is too large, reduce conv_thr". I am >> using conv_thr = 1.0d-8 which is generally sufficient, so I increased >> the >> parameter upscale (from 10.0 to 100.0) in &IONS to reduce the the >> threshold during relaxation. This lead to the convergence till the last >> ionic iteration which was converged to sufficient accuracy, when again >> the >> same error message occurred. The forces then are >> Total force = 0.000136 Total SCF correction = 0.000016 >> SCF correction compared to forces is too large, reduce conv_thr >> >> There has been a recent discussion on the topic. From that, I gathered >> that the subsequent relaxations after this error message are not >> reliable. >> So my question is whether the forces are reliable in this last >> iteration? >> Or do I need to further reduce the conv_thr and re-run the whole >> calculation? >> >> Thanks for the help, >> Madhura. >> >> > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum > -- Madhura Marathe, PhD student, TSU, JNCASR, Bangalore. India. Phone No: +91-80-22082835
