about external pressure

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wjfriend · #1 Post by **wjfriend** » Thu Feb 16, 2012 10:23 am

Hi, I want to applied a specific hydrostatic pressure (say 10KB) in the structure to calculate the energy and correspoding volume.
I set ISIF=3
PSTRESS=100 (for compression) and -100 (for tension).
I also set the ENCUT=1.3*ENMAX
I found the results: energy and volume for compression and tension are the same, and the external pressure is -1.5KB for PSTRESS=100, and 1.5KB for PSTRESS=-100.
Please let me know is ISIF=3 is right? and how to expalin my calculation results. Thanks so mcuh.

#2 Post by **admin** » Thu Feb 16, 2012 3:12 pm

You should fix the cell volume (e.g. ISIF=2). Then you will see the effect of applied pressure in OUTCAR (external pressure).
Cf. also the previous post:
http://cms.mpi.univie.ac.at/vasp-forum/ ... .php?4.862

wjfriend · #3 Post by **wjfriend** » Thu Feb 16, 2012 8:11 pm

Hi head admin,

Thank you for your reply. I am still confused about setting ISIF=2.
In my case, the volume is 100 at zero pressure, now I apply hydrostatic pressure to the structure, so the volume should be decreased. I need to find this volume change and the correspoing internal energy. If I set ISIF=2, the volume is fixed, then how can I get the volume change.
Thanks so much. I have struggled on this for a while and still not clear.

guo,huaihong · #4 Post by **guo,huaihong** » Sat Apr 28, 2012 4:00 am

[quote author=2.
In my case, the volume is 100 at zero pressure, now I apply hydrostatic pressure to the structure, so the volume should be decreased. I need to find this volume change and the correspoing internal energy. If I set ISIF=2, the volume is fixed, then how can I get the volume change.
Thanks so much. I have struggled on this for a while and still not clear.[/quote]
Hi,friends,I also have the same problem as you. Do you know the answer now? thanks in advance!