[Pw_forum] optimization and pseudo potentials

[James Mao]

Dear users,

 

I am trying to calculate NMR chemical shifts by GIPAW for a crystal (with
atoms Al, P, O). The pps I used 

with GIPAW are "pbe-tm-gipaw-dc" sets. I did get reasonable results.

 

For a second step I tried to optimize the structure. I noticed if I still
used the gipaw pps, the optimization 

process is completely wrong. In vc-relax calculations the cell volume keeps
shrinking to 67% of original 

volume (which is from experimental structure). While I changed the pps to
"pbe-n-kjpaw" set, vc-relax 

gave reasonable results.

 

I would be very thankful if someone can explain a little bit for me what
kind of pps are not suitable for 

optimization so in future I can avoid similar mistake? Any helps will be
greatly appreciated.

 

Best regards,

James Mao

 

Postdoc associate

Department of Chemistry,

University of Pittsburgh

 

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