## External pressure in NPT run

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### External pressure in NPT run

Hello,

I am running MD simulation with NPT ensemble using VASP. I refer the community forum questions and find the information, how to get the value of external pressure from NPT run OUTCAR file,

grep "Total+kin" OUTCAR| awk 'BEGIN {p=0.} {p+=(\$2+\$3+\$4)/3.} END {print "pressure (kB):",p}'

I used this command, but its printing only one pressure value, I am not clear whether its average external pressure during the run or last step pressure?

How to get the value of external pressure at each MD step? I think we need these values to check the convergence of set external pressure?

Here is my INCAR file:

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Graphene !title
Starting parameters:
ISTART = 0 #0-new, 1- Continuation job , 2-samecut
NWRITE = 0 ! verbosity for OUTCAR
LWAVE = .TRUE. ! write WAVECAR?
LCHARG = .FALSE. ! write CHGCAR?
LVTOT = .FALSE. ! write LOCPOT?
Electronic relaxation
ALGO = Accurate ! coupled to IALGO
IALGO = 48 ! 8: conjugate gradient, 48: DIIS
ENCUT = 520 ! kinetic energy cut-off (see Sholl/Steckel Ch 3.2)
ISMEAR = 0 ! electron smearing method. -1: Fermi 0: Gaussian 1..N: Methfessel-Paxton
SIGMA = 0.05 ! smearing parameter (see Sholl/Steckel Ch 3, p 11.)
ISYM = 0
PREC = normal ! coupled to ENCUT
LREAL = auto ! work in real or recipricol space (see Sholl/Steckel Ch 3.1)
EDIFF = 1.0E-5 ! elec. struc. converged when diff. btwn subsequent steps is less than this.
ISPIN = 2 ! spin polarization? 1=no, 2=yes.
LVDW = .TRUE.
IVDW = 1
NCORE = 4
Ionic relaxation
NSW = 2000
IBRION = 0
ISIF = 3
POTIM = 0.5 ! scaling constant
EDIFFG = 1.0E-4 ! geom. converged when all forces are lower than abs. value (eV/Ang
MDALGO = 3
PSTRESS = 0.05
LANGEVIN_GAMMA = 10 10 10
LANGEVIN_GAMMA_L = 1
PMASS = 35
TEBEG = 298 ; TEEND = 298 ! temperature

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Any help is really appreciated.

Sahida
Ph.D. Candidate
Simon Fraser University
13450 102 Avenue, Surrey(BC)-V3T 0A3
skureshi
Newbie

Posts: 3
Joined: Fri Jul 15, 2016 7:06 pm

### Re: External pressure in NPT run

External pressure in each MD step:
grep Total+kin OUTCAR | awk 'BEGIN {print "# step","pressure (kBar)" } {print NR, (\$2+\$3+\$4)/3 }'