Thanks Carlo. The system is not metallic. Just as I mentioned, only atom types it includes are H, C, N, O, S, P, F.
I noticed last month Peng reported a similar observation: http://www.democritos.it/pipermail/pw_forum/2012-September/025080.html In his case he used smearing, and kpoints(4,4,3). His PP is also NC pbe (pbe-n-kjpaw), and observed a minimum at ecut=80, very similar to my case. Best, James -----Original Message----- From: pw_forum-bounces at pwscf.org [mailto:pw_forum-boun...@pwscf.org] On Behalf Of Carlo Nervi Sent: Tuesday, October 09, 2012 3:07 AM To: pw_forum at pwscf.org Subject: Re: [Pw_forum] about ecutwfc convergence for total energy Hi, as far as i know it seems a problem related with bands, so low number of k-points (for insulators). I would suggest in any cases to try to use a couple of k-points. Another important point: are you sure your system is not metallic? In this case you could try smearing. HTH, Carlo Il 08/10/2012 17.05, James Mao ha scritto: > Hi all, > > I am a little bit confused about ecutwfc convergence. I am working on > calculating NMR of a crystal structure. Before that I need test SCF > energy convergence. > However I noticed the total energy is not convergent with respect to > ecutwfc. > > It reached minimum at ecutwfc=90 then began oscillating up and down. > > Ecutwfc Total Energy > > 70 -3249.733804 > > 80 -3250.674250 > > 90 -3250.827326 > > 100 -3250.661301 > > 120 -3250.346091 > > 160 -3250.582989 > > 200 -3250.395401 > > I think higher ecutwfc means more basis functions, therefore should > always result in a lower total energy. If I am wrong, should I keep > increasing ecutwfc? > > The PP I used is (pbe-tm-new-gipaw-dc.UPF), the atoms include C, O, N, > F, S, H, P. > > Since PP is NC, I left ecutrho default. And since the cell is pretty > big (a~10, b~16, C~15), I only calculated at gamma point. > > Any hint is helpful! Thanks. > > Best, > > James Mao > > ---------------------------------- > > Postdoc, Department of Chemistry, University of Pittsburgh > > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum > -- ------------------------------------------------------------ Prof. Carlo Nervi carlo.nervi at unito.it Tel:+39 0116707507/8 Fax: +39 0116707855 - Dipartimento di Chimica, via P. Giuria 7, 10125 Torino, Italy. http://lem.ch.unito.it/ _______________________________________________ Pw_forum mailing list Pw_forum at pwscf.org http://pwscf.org/mailman/listinfo/pw_forum