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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal>Hi all,<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I am a little bit confused about ecutwfc convergence. I am working on calculating <br>NMR of a crystal structure. Before that I need test SCF energy convergence. <br>However I noticed the total energy is not convergent with respect to ecutwfc. <o:p></o:p></p><p class=MsoNormal>It reached minimum at ecutwfc=90 then began oscillating up and down. <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Ecutwfc Total Energy<o:p></o:p></p><p class=MsoNormal>70 -3249.733804<o:p></o:p></p><p class=MsoNormal>80 -3250.674250<o:p></o:p></p><p class=MsoNormal>90 -3250.827326<o:p></o:p></p><p class=MsoNormal>100 -3250.661301<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>120 -3250.346091<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>160 -3250.582989<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>200 -3250.395401<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I think higher ecutwfc means more basis functions, therefore should always result<br>in a lower total energy. If I am wrong, should I keep increasing ecutwfc?<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The PP I used is (pbe-tm-new-gipaw-dc.UPF), the atoms include C, O, N, F, S, H, P.<o:p></o:p></p><p class=MsoNormal>Since PP is NC, I left ecutrho default. And since the cell is pretty big (a~10, b~16, C~15), <br>I only calculated at gamma point.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Any hint is helpful! Thanks.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Best,<o:p></o:p></p><p class=MsoNormal>James Mao<o:p></o:p></p><p class=MsoNormal>----------------------------------<o:p></o:p></p><p class=MsoNormal>Postdoc, Department of Chemistry, University of Pittsburgh<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>