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 -------------- next part -------------- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20121008/59046c16/attachment-0001.html
