[Pw_forum] conv_thr for forces for relaxing ions
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 = 0.16 >> 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
[Pw_forum] conv_thr for forces for relaxing ions
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 = 0.16 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. -- Madhura Marathe, PhD student, TSU, JNCASR, Bangalore. India. Phone No: +91-80-22082835
[Pw_forum] conv_thr for forces for relaxing ions
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 = 0.16 > 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. > >
