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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal>Dear users,<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I am trying to calculate NMR chemical shifts by GIPAW for a crystal (with atoms Al, P, O). The pps I used <o:p></o:p></p><p class=MsoNormal>with GIPAW are “pbe-tm-gipaw-dc” sets. I did get reasonable results.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>For a second step I tried to optimize the structure. I noticed if I still used the gipaw pps, the optimization <o:p></o:p></p><p class=MsoNormal>process is completely wrong. In vc-relax calculations the cell volume keeps shrinking to 67% of original <o:p></o:p></p><p class=MsoNormal>volume (which is from experimental structure). While I changed the pps to “pbe-n-kjpaw” set, vc-relax <o:p></o:p></p><p class=MsoNormal>gave reasonable results.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I would be very thankful if someone can explain a little bit for me what kind of pps are not suitable for <o:p></o:p></p><p class=MsoNormal>optimization so in future I can avoid similar mistake? Any helps will be greatly appreciated.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Best regards,<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 associate<o:p></o:p></p><p class=MsoNormal>Department of Chemistry,<o:p></o:p></p><p class=MsoNormal>University of Pittsburgh<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>