Dears, if you are testing the mesh cutoff you should also be careful in using a cutoff high enough to avoid the eggbox effect. See here:
http://personales.unican.es/junqueraj/JavierJunquera_files/Metodos/Convergence/Convergence.html Best, Zeila --------------------------------------------------------------- Dr. Zeila Zanolli ETSF Research Team Leader (http://www.etsf.eu/) Mobile: +32 487 556699 e-mail: [email protected] web: http://zeilazanolli.wordpress.com/home ResearcherID: http://www.researcherid.com/rid/F-9568-2010 ---------------------------------------------------------------- On Wed, Aug 12, 2015 at 7:52 PM, Ludwig, Stephan <[email protected]> wrote: > Thank you Zacharias > > > -----Original message----- > From: [email protected] <[email protected]> > Sent: Wednesday 12th August 2015 19:45 > To: [email protected] > Subject: RE: [SIESTA-L] When is convergence reached? > > Try to find the convergence in terms of energy per atom. What you will > find is that your energy is converged with accuracy less than 1meV/atom. > This accuracy is good enough for band structure calculations. Therefore, > convergence has already been reached for a 200 mesh cutoff. > > Zacharias Fthenakis > > >> Hi, >> >> thank you for the reply my unit cell is rather big (at least for a solid). >> Its an organic salt with 236 atoms. >> >> Cell volume = 2905.615438 Ang**3 >> >> : Cell vector modules (Ang) : 32.783000 11.179003 7.999052 >> >> >> >> In the first step I want to study bandstructure DOS and PDOS. >> >> Later optical excitations. >> >> >> >> Can you tell when I can call the system convergent wrt the total energy. >> >> >> >> Thanks and Regards >> >> Stephan >> >> >> >> -----Original message----- >> From: [email protected] <[email protected]> >> Sent: Tuesday 11th August 2015 18:52 >> To: [email protected] >> Subject: Re: [SIESTA-L] When is convergence reached? >> >> >> Hi Stephan, >> it depends on how big is your unit cell and what you want to study. >> >>> Hi, >>> >>> I've a question concerning the convergence criterion. >>> >>> Let's say I want to examine convergence of the total energy a system >>> with >>> respect to the meshcutoff. >>> >>> When is convergence reached? Is it reached when there is no change in >>> the >>> first digit after the comma >>> >>> like in the following example: >>> >>> meshcutoff total energy >>> >>> 150 -42994.1019 >>> >>> 170 -42994.116 >>> >>> 190 -42994.127 >>> >>> 210 -42994.133 >>> >>> >>> >>> or is it usefull to continue the test till there is no change in the >>> second digit after the comma? >>> >>> What is a sensible criterion for convergence? >>> >>> >>> >>> Thanks and regards >>> >>> >>> >>> Stephan Ludwig >>> >>> >> >> >> ********************************************************* >> Dr Zacharias G. Fthenakis >> Research Associate >> Institute of Electronic Structure and Laser (I.E.S.L.) >> Foundation for Research and Technology Hellas (FO.R.T.H.) >> Vassilika Vouton P.O. Box 1527 71003 Heraklion Crete Greece >> Phone +30 2810 391824 >> FAX +30 2810 391305 >> webpage: http://esperia.iesl.forth.gr/˜fthenak >> ********************************************************** >> >> >> > > > ********************************************************* > Dr Zacharias G. Fthenakis > Research Associate > Institute of Electronic Structure and Laser (I.E.S.L.) > Foundation for Research and Technology Hellas (FO.R.T.H.) > Vassilika Vouton P.O. Box 1527 71003 Heraklion Crete Greece > Phone +30 2810 391824 > FAX +30 2810 391305 > webpage: http://esperia.iesl.forth.gr/˜fthenak > ********************************************************** >
