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 -------------------------------------------------
