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 *********************************************************
