Phase transition under pressure?

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new_986
Posts: 76
Joined: Wed Aug 04, 2010 9:27 pm

Phase transition under pressure?

Post by new_986 » Mon Oct 29, 2018 8:42 am

Hello everybody
I am trying to investigate properties of a perovskite compound, experimentally phase undergoes through transition at 4 GPa,
I also increase the pressure and I do relaxation to the unit cell for all pressures up to 10 GPa, but my structure keeps the same which is cubic (doesn't undergo phase transition)
see the input file please

optcell 2
prtcif 1

prtgeo 1
#tsmear 0.02
ndtset 10
strtarget1 -3.39892892272001E-05 -3.39892892272001E-05 -3.39892892272001E-05 0 0 0
strtarget2 -6.79785784544003E-05 -6.79785784544003E-05 -6.79785784544003E-05 0 0 0
strtarget3 -0.0001019679 -0.0001019679 -0.0001019679 0 0 0
strtarget4 -0.0001359572 -0.0001359572 -0.0001359572 0 0 0
strtarget5 -0.0001699464 -0.0001699464 -0.0001699464 0 0 0
strtarget6 -0.0002039357 -0.0002039357 -0.0002039357 0 0 0
strtarget7 -0.000237925 -0.000237925 -0.000237925 0 0 0
strtarget8 -0.0002719143 -0.0002719143 -0.0002719143 0 0 0
strtarget9 -0.0003059036 -0.0003059036 -0.0003059036 0 0 0
strtarget10 -0.0003398929 -0.0003398929 -0.0003398929 0 0 0
#relaxation
ionmov 2
ntime 100
tolmxf 5.0d-6
dilatmx 1.1
#Cell and atoms definition
acell 3*6.0045791044 Angstr
rprim 0.0 0 1
1 0.0 0
0 1 0
ntypat 3 natom 5 typat 1 2 3 3 3
xangst 0.0000000000E+00 0.0000000000E+00 0.0000000000E+00
3.0022903116E+00 3.0022903116E+00 3.0022903116E+00
3.0022903116E+00 0.0000000000E+00 3.0022903116E+00
3.0022903116E+00 3.0022903116E+00 0.0000000000E+00
0.0000000000E+00 3.0022903116E+00 3.0022903116E+00
znucl 55 82 35 nband 40

#Basis definitions
ecut 45
ecutsm 0.5
pawecutdg 100

#SCF cycle parameters
tolvrs 1.0d-15
nstep 200
iscf 5
#K-points and sym
#nsym 0
occopt 1
ngkpt 6 6 6
nshiftk 4
shiftk 0.5 0.5 0.5
0.5 0.0 0.0
0.0 0.5 0.0
0.0 0.0 0.5

#I/O parameters
prtwf 1 prtden 0 prteig 0
getwfk -1
timopt 2


Any help please ?

Nawzad

gregory
Posts: 5
Joined: Fri Jan 30, 2015 4:13 pm

Re: Phase transition under pressure?

Post by gregory » Fri Nov 30, 2018 2:52 pm

Dear Nawzad
ABINIT performs the structural optimizations by keeping the symmetries of the initial structure. It seems that your system has the cubic symmetry (Pm-3m). If you do not allow ABINIT to leave this space group, it is normal that the system remains always cubic. Simply break the symmetries by, e.g., displacing randomly all the atoms by very small displacements, and then restart your optimization: if the system wants to be cubic, the optimization will bring you back to the cubic structure; if it wants to be something else, ABINIT should normally lead the system to the energy minimum which is the closest from the initial structure.
Gregory

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new_986
Posts: 76
Joined: Wed Aug 04, 2010 9:27 pm

Re: Phase transition under pressure?

Post by new_986 » Sat Dec 01, 2018 10:57 am

gregory wrote:Dear Nawzad
ABINIT performs the structural optimizations by keeping the symmetries of the initial structure. It seems that your system has the cubic symmetry (Pm-3m). If you do not allow ABINIT to leave this space group, it is normal that the system remains always cubic. Simply break the symmetries by, e.g., displacing randomly all the atoms by very small displacements, and then restart your optimization: if the system wants to be cubic, the optimization will bring you back to the cubic structure; if it wants to be something else, ABINIT should normally lead the system to the energy minimum which is the closest from the initial structure.
Gregory

Dear Gregory
Thanks for the reply
to what direction should I displace atoms, any direction? all direction ? or a specific direction? if a specific direction, x , y or z?

best regards

Nawzad

ebousquet
Posts: 398
Joined: Tue Apr 19, 2011 11:13 am
Location: University of Liege, Belgium

Re: Phase transition under pressure?

Post by ebousquet » Wed Dec 05, 2018 10:05 am

Dear Nawzad,
I would say the most general directions to break all the symmetries.
Best wishes,
Eric

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new_986
Posts: 76
Joined: Wed Aug 04, 2010 9:27 pm

Re: Phase transition under pressure?

Post by new_986 » Mon Dec 17, 2018 10:08 am

ebousquet wrote:Dear Nawzad,
I would say the most general directions to break all the symmetries.
Best wishes,
Eric

Thanks Eric
I will try that

Nawzad

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