Dear Ulrich, According you instruction, I found the "Tot" line following the "atomic forces (eV/Ang)" line, which I copied here.
siesta: Atomic forces (eV/Ang): ---------------------------------------- Tot 0.039922 0.040911 -0.040042 ---------------------------------------- Max 0.046196 Res 0.019793 sqrt( Sum f_i^2 / 3N ) ---------------------------------------- Max 0.046196 constrained May I ask you some questions regarding this? 1) Does the three number in the "Tot" line mean the force in x, y, z direction or not? 2) As you mentioned "The sum of all forces should be zero", how do you define "zero" here? In other words, how small the sum of the total forces can be treated as "zeros" here? Thanks a lot. On Wed, Aug 10, 2011 at 3:43 AM, Ulrich Biedermann <[email protected]>wrote: > Dear Lily, > > the best approach is to check convergence of your property of interest with > mesh-cutoff, > which often is better (at smaller cutoff) than the convergence of total > energy. The reason is systematic error cancellation. > > However, as "early warning indicator" I keep an eye on the line " Tot " at > the end of the "atomic forces (eV/Ang)" listing in the output file. The sum > of all forces should be zero. If this is not the case, the fores suffer > from numerical problems often related to a small mesh-cutoff (e.g. eggbox > effect). In these cases geometry optimization also becomes difficult (takes > very many cycles with little change in energy and geometry). > > Regards, Ulrich. > > ----- Original Message ----- > From: lily zheng > [mailto:[email protected]] > To: [email protected] > Sent: Tue, 09 Aug 2011 > 22:52:44 +0200 > Subject: [SIESTA-L] question about meshcutoff > > > > Dear All, > > > > Just got a question about meshcutoff. For the general case, if we use > too > > small meshcutoff, what output would become strange or any signs which > > indicates that the meshcutoff used is too small? > > > > > > thanks > > > > Lily > > > > --- > Max-Planck-Institut für Eisenforschung GmbH > Max-Planck-Straße 1 > D-40237 Düsseldorf > > Handelsregister B 2533 > Amtsgericht Düsseldorf > > Geschäftsführung > Prof. Dr. Jörg Neugebauer > Prof. Dr. Dierk Raabe > Prof. Dr. Martin Stratmann > Dipl.-Kfm. Herbert Wilk > > Ust.-Id.-Nr.: DE 11 93 58 514 > Steuernummer: 105 5891 1000 > ------------------------------------------------- > >
