ear Asha gupta, if your are sure that the system is an non-magnetic insulator then there is no point in using smearing and include more bands. Your smearing_width looks very small to me, especially with methfessel-paxton which, being non positive definite, could give problems of negative occupations if the k-point sampling is not good enough. If you want to keep the smearing use marzari-vanderbilt ... or even plain gaussian smearing ... for an insulator it should not matter anyway. As I said you may want to try mixing_mode='local-TF'.
stefano Quoting Asha gupta <toashagupta at gmail.com>: > Dear Stefano, > i am using the following: > &system: ibrav=0, nat= 98, ntyp=4, ecutwfc = 30.0,ecutrho = > 180.0,occupations='smearing', smearing='methfessel-paxton', > degauss=0.003,nbnd=500, > &electrons: conv_thr = 1.0e-5,mixing_beta = 0.1, > K_points sampling: 4 4 4 0 0 0, > the system is insulator and non-magnetic for sure. the number of bands are > little higher than what is actually required for an insulator. Tha same k > points sampling for smaller similar system gave results which tallies well > reported data. > Shall i stop the calculation or let it run to completion? after compleion, > then i can take the new refined data as my input and reduced conv_thr and > re-run the calculation again. > regards > artee > department of physics > Bhavnagar university > india > > On 3/22/09, Stefano de Gironcoli <degironc at sissa.it> wrote: >> >> dear artee sharma, >> >> conv_thr=1.0e-5 is a rather large value, acceptable if you just want >> the energy but not if you want forces. 1.0e-6 is the default and for >> relaxations one rather tends to reduce it... >> >> Convergence for large systems (especially inhomogeneous metallic ones) >> may be slow. mixing_mode='local-TF' usually helps in these cases. are >> you using it ? >> >> Even when the first scf convergence is painfully slow the subsequent >> ones should be better as potential and wfcs are extapolated from >> previous steps. check that you are indeed using these extrapolations >> (should however be the default for relaxation, so probably you do). >> >> Sometime when a system does not want to converge it's trying to tell >> you something ... Is it a magnetic or metallic system ? are you using >> smearing ? are you sure the number of bands and your k-point sampling >> is accurate enough ? >> >> hope this helps, >> stefano >> >> Stefano de Gironcoli - SISSA and DEMOCRITOS >> >> >> Quoting artee sharma <mailtoartee at gmail.com>: >> >> > Dear Stefano. >> > thanks for reply. my conv_thr in input file is 1.0e-5? i have a large >> >> > system, takes too much time to convarage, so kept it low. Shall i >> decrease >> > it by further one order? >> > latest output is showing: >> > Total force = 0.023049 Total SCF correction = 0.002483 >> > so i think my system has not converged yet, force is high. >> >> > regards >> > artee sharma >> > Department of physics >> > Bhavnagar University >> > India >> > >> > >> > >> > >> > On Sat, Mar 21, 2009 at 11:46 AM, Stefano de Gironcoli >> > <degironc at sissa.it>wrote: >> > >> >> I think it might be better to stop it. According to the message the >> forces >> >> you are calculating may be not accurate and any further relaxation based >> on >> >> them is not likely to improve your geometry. >> >> >> >> However, are you sure your system is not yet relaxed enough ? >> >> What is your conv_thr and your force threshold ? >> >> >> >> stefano de Gironcoli - SISSA & DEMOCRITOS >> >> >> >> PS: don't forget to provide your affiliation >> >> >> >> >> >> >> >> >> >> >> >> Quoting artee sharma <mailtoartee at gmail.com>: >> >> ** >> >> >> >> >> >> ---------------------------------------------------------------- >> >> SISSA Webmail https://webmail.sissa.it/ >> >> Powered by Horde http://www.horde.org/ >> >> >> >> >> >> >> > >> >> >> >> ---------------------------------------------------------------- >> SISSA Webmail https://webmail.sissa.it/ >> Powered by Horde http://www.horde.org/ >> >> >> _______________________________________________ >> Pw_forum mailing list >> Pw_forum at pwscf.org >> http://www.democritos.it/mailman/listinfo/pw_forum >> > ---------------------------------------------------------------- SISSA Webmail https://webmail.sissa.it/ Powered by Horde http://www.horde.org/
