Hi, >Just to double-check. Is charge density cutoff 4 times that planewave cutoff?
I think that this hits on the issue... The Zn.pz-nc.UPF has a sharp core correction. The FFT/Density grid needs to be increased significantly, here is a plot of from 4x to 20x ecutwfc for the case with and without a core correction in Zn. I think this is the cause of the odd *ecutwfc* shown by William Parker. http://dl.dropbox.com/u/8094696/Znplot.pdf So, in this case, no, the density cutoff needs to be higher: Eric On 10/19/2011 08:47 PM, Nichols A. Romero wrote: > The behavior here is what I might expect for a real-space DFT code, > but V_NL is evaluated in reciprocal space right (we don't have > real-space projectors)? > > Just to double-check. Is charge density cutoff 4 times that planewave cutoff? > > > On Wed, Oct 19, 2011 at 2:51 PM, William Parker<wparker at anl.gov> wrote: >> Dear Yun Song and interested parties, >> >> The possibility of a phonon test case in ZnO piqued my curiosity so I >> decided to have a go at it. I find a very odd convergence pattern with >> these two pseudopotentials in this system--the total energy has a damped >> sinusoidal decay with increasing cutoff: >> (selecting the maxima and minima at 10 Ry sampling) >> >> E_cutoff (Ry) E_total (Ry) >> 100 -338.741 >> 160 -338.660 >> 210 -338.675 >> 290 -338.665 >> 370 -338.668 >> 400 -338.667 >> >> Figure here: >> https://wiki.alcf.anl.gov/wparker/images/b/b5/ZnO_ecut_convergence_lda_ncpp.png >> Details here: >> https://wiki.alcf.anl.gov/wparker/index.php/Zinc_Oxide_Parameter_Convergence >> >> I have never encountered this kind of behavior with norm-conserving >> pseudopotentials before. At worst, I've seen little steps in an otherwise >> smooth convergence to a value. The eigenvalues at the various k-points >> don't appear to have any ghost states that come and go with cutoff. Has >> anyone observed this kind of oscillation in the total energy with increasing >> plane-wave cutoff before? What gives rise to it? >> >> --William >> >> ********************************************************* >> William D. Parker >> Computational Postdoctoral Fellow fax: (630) 252-4798 >> MSD-212, Rm. C-215 >> Argonne National Laboratory >> 9700 S. Cass Ave. >> Argonne, IL 60439 >> ********************************************************* >> >> >> >> >> _______________________________________________ >> Pw_forum mailing list >> Pw_forum at pwscf.org >> http://www.democritos.it/mailman/listinfo/pw_forum >> > >
