ABINIT Discussion Forums

Dear colleagues,

I'm trying to reproduce phonon frequencies at the X point of the BZ of ZrO2 fluorite. However, whatever I tried concerning the response function calculation, I failed.
Therefore, I am unsure if I am using the correct structure. Could anyone, please, help me and confirm that I'm using the correct structure. My input file is bellow.

Thank you all in advance!

Yours
Igor Lukacevic



# Crystalline ZrO2 - fluorite : computation of the response to atomic displacements, at q=X

ndtset 2

#Ground state calculation
kptopt1 1 # Automatic generation of k points, taking
# into account the symmetry
tolvrs1 1.0d-15 # SCF stopping criterion
iscf1 5 # Self-consistent calculation, using algorithm 5

#Response Function calculation : electric field perturbation and phonons
rfphon2 1 # Activate the calculation of the atomic dispacement perturbations
rfatpol2 1 3 # All the atoms will be displaced
rfdir2 1 1 1 # All directions are selected. However, symmetries will be used to decrease
# the number of perturbations, so only the x electric field is needed
# (and this explains why in the second dataset, rfdir was set to 1 0 0).
nqpt2 1
qpt2 0.0 0.5 0.5 # This is a calculation at X point

getwfk2 1 # Uses as input wfs the output wfs of the dataset 1

kptopt2 3 # Automatic generation of k points,
# no use of symmetries to decrease
# the size of the k point set.
tolvrs2 1.0d-8
iscf2 5 # Self-consistent calculation, using algorithm 5

#######################################################################
#Common input variables

#Definition of the unit cell
acell 3*9.47118842767
rprim 0.0 0.5 0.5
0.5 0.0 0.5
0.5 0.5 0.0

#Definition of the atom types
ntypat 2
znucl 40 8 8

#Definition of the atoms
natom 3
typat 1 2 2
xred 0.00 0.00 0.00
0.25 0.25 0.25
0.75 0.75 0.75

#Gives the number of band, explicitely (do not take the default)
nband 14

#Exchange-correlation functional
ixc 3

#Definition of the planewave basis set
ecut 100
ecutsm 0.5

#Definition of the k-point grid
ngkpt 3*10
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

#Definition of the SCF procedure
nstep 100
diemac 4.0

Hello Igor,

Your input looks more or less ok - what do you mean you "failed" to do the phonon run?

1) use iscf 7, it's better
2) your ecut is huge

Matthieu

PS: znucl only need 2 values (nytpat=2)

Dear prof. Verstraete,

mverstra wrote:PS: znucl only need 2 values (nytpat=2)

Understood.

mverstra wrote:Your input looks more or less ok - what do you mean you "failed" to do the phonon run?

1) use iscf 7, it's better
2) your ecut is huge

Matthieu

It's not that the run failes - abinit works perfectly - but by "failed" I meant that, although I get an almost perfect agreement for phonons at Gamma point (and Z* and diel. const.), at any other point in the BZ I obtain almost complete inagreement. I have already posted my problems in the Response function section, but all the suggestions (ranging from rfasr and various tols to anaddb input file) failed to correct these errors.

I supposed that problem lies somewhere else and wanted to check if the structure itself is correct. For I have run out of ideas how to reproduce phonon dispersions in ZrO2 fluorite.

1) just to mention: iscf 5 is a leftover from the relaxation, which worked nicely with it; rf calc. works good with it also.
2) I deliberately put ecut to high, since I wanted to check the convergence of phonon freqs (this was a desperate run). Although I knew that good results are obtained with even ecut 40 for Teters' extended norm pseudos. I was just trying all the possibilities.


Thank You very much for confirmation! But this has two sides, since now I know that the structure is not the reason for terrible phonon dispersions.

Yours,

Igor Lukacevic