[QE-users] non-convergent scf calculation on organometal perovskite structure
Julien Barbaud
julien_barbaud at sjtu.edu.cn
Fri Feb 22 08:14:43 CET 2019
Thank you Pietro for your experienced advices,
I had tried to increase the kmesh size before but only up to sizes of
7x7x7. Reading your suggestions, I ran additional tests up to 10x10x10
but this did not show any sign of improvement on 70 iterations. As shown
in file kmesh.png, the estimated accuracy is still stagnating after a
while and the 10*10*10 is actually giving arguably worse results than
the 9*9*9 although this is most likely not significant. Actually, some
papers report DFT simulation of MAPbI3 using 6x6x6 kmesh, or even single
gamma-point calculation, so I guess this should not be the obstacle to
convergence here.
Regarding the orientation of MA, I definitely agree with you, but I
don't think it can prevent the system from converging ? Sure enough, it
can have an important influence on the precision of the results in later
uses. But I would like to achieve convergence on this simple single cell
first, before building up supercells to take more complex effects into
account. A crystal with perfectly aligned MA might not reflect the true
experimental system, but it should still be a possible configuration
that the QE code should be able to compute, am I wrong ?
As to your suggestion on VdW corrections, I just gave it a try, but
unfortunately, this is unconclusive too. I report the accuracy at each
iteration in vdw.png. Again, the accuracy stops improving after a while.
Plese note that I had to change my pseudo-potentials to use 'xdm'
correction (which only supports PAW PP). the input file for this test is
included as attached file
Julien
Le 21/02/2019 à 16:35, Pietro Davide Delugas a écrit :
> Hi
>
> Have you tried to increase the k_point mesh ? 4 4 4 seems a little
> bit lax as mesh for MAPbI3.
> If I remember well I am afraid that to get convergence you will need
> something like 10X10X10.
> As for the structure neighboring methylammoniums like to orient
> differently one from the other, you should probably use a larger
> cell. Also consider to add some correction for van der Waals
> interactions see here (
> https://www.quantum-espresso.org/Doc/INPUT_PW.html#idm45922794348896)
>
> hope it helps
> Pietro
>
>
> On 02/21/2019 04:17 AM, Julien Barbaud wrote:
>> Dear users,
>>
>>
>> I am new to QE, and trying to run a simple scf calculation on a
>> CH3NH3PbI3 crystal (semi-conducting material). I am using ultrasoft
>> pseudopotentials based on the exchange-correlation functionnal PBEsol.
>>
>> I set up a first input, with values of parameters inspired from
>> literature on the subject. However, I could not reach convergence
>> after 100 iterations. The estimated error was actually "exploding" to
>> very high values, indicating a serious problem. I tried several
>> changes but was unsuccessful:
>>
>> * varying plane-wave cutoff energy does not solve the problem (cf
>> attached ecut.png, giving the estimated error as a function of
>> the number of iterations. It is shown here only on the first 15
>> iterations as the results pretty much only stall from there)
>> * varying cutoff energy for charge (cf ecutrho.png)
>> * taking larger k-point sampling (not shown)
>> * I also read that for metallic or "close to metallic conductors",
>> there might be problems with the first unoccupied states that can
>> be solved by adding a few empty bands. My system being a
>> semi-conductor, I tried adding additional bands using a m-p
>> smearing but no improvement was found (not shown)
>>
>>
>> The only change that I found effective was to reduce the mixing_beta
>> factor.
>>
>>
>> It effectively prevents the error from diverging to very large
>> values, but I still do not reach convergence, even after longer
>> iterations. I tried much smaller values of mixing beta which improves
>> the final value of the error, but I still cannot reach convergence on
>> 100 iterations. As shown in the mixbeta2_zoom.png, the error reduces
>> to smaller values around ~1e-5~1e-6, but it keeps stalling after a
>> while. I do not observe a well-converging behaviour for any value.
>>
>>
>> I attached the "default version" of my script on which the various
>> modifications described above have been independently performed. I
>> obtained the geometry from a CIF file in literature and checked it
>> with visualization software; it seems perfectly ok as far as I can tell.
>>
>>
>> Any insight on what I did wrong would be really helpful. I suspect a
>> shameful beginner mistake, but can not find it out.
>>
>>
>> Thanks in advance,
>>
>> Julien barbaud
>>
>>
>> P.S: this is my first time posting on this user list. Please let me
>> know if my question is not suitable for it, or can be improved either
>> in its content or presentation. I will gladly take any recommandation
>> into account in order not to negatively impact the quality of this
>> user list !
>>
>>
>>
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>
>
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&CONTROL
pseudo_dir = "/home/julien_barbaud/QUANTUM_ESPRESSO/Program/qe-6.3/pseudo"
calculation = 'scf'
outdir= "./out"
tstress=.TRUE.
tprnfor=.TRUE.
/
&SYSTEM
nat= 12
ntyp= 5
ibrav= 0
ecutwfc= 45, ecutrho = 450
vdw_corr='xdm', xdm_a1=0.0000, xdm_a2=4.1503
/
&ELECTRONS
mixing_beta = 0.00075
conv_thr = 1.0d-7
electron_maxstep = 100
/
&IONS
/
&CELL
/
ATOMIC_SPECIES
C 12.011 C.pbesol-n-kjpaw_psl.1.0.0.UPF
N 14.007 N.pbesol-n-kjpaw_psl.1.0.0.UPF
H 1.008 H.pbesol-kjpaw_psl.0.1.UPF
Pb 207.2 Pb.pbesol-dn-kjpaw_psl.1.0.0.UPF
I 126.90 I.pbesol-n-kjpaw_psl.1.0.0.UPF
CELL_PARAMETERS angstrom
6.28880000 0.00000000 0.00000000
0.00154263 6.22876981 0.00000000
0.13973295 -0.00036613 6.37255819
ATOMIC_POSITIONS angstrom
C 5.68762816 6.22746232 2.91755469
N 0.76248596 -0.00015695 3.49068983
H 5.76522586 6.22643528 1.82113056
H 5.15723272 0.90114080 3.25657478
H 5.15968675 5.32511200 3.25829538
H 1.30458379 0.84536565 3.19592078
H 1.30663813 5.38278144 3.19763499
H 0.76813187 0.00090438 4.53227809
Pb 2.93516392 3.11390239 6.22995946
I 2.64234654 3.11409882 3.02788916
I 2.51578467 6.22849954 0.15080022
I 5.99299067 3.11401602 5.87855111
K_POINTS automatic
4 4 4 0 0 0
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&CONTROL
pseudo_dir = "/home/julien_barbaud/QUANTUM_ESPRESSO/Program/qe-6.3/pseudo"
calculation = 'scf'
outdir= "./out"
tstress=.TRUE.
tprnfor=.TRUE.
/
&SYSTEM
nat= 12
ntyp= 5
ibrav= 0
ecutwfc= 30, ecutrho = 300
nbnd= 30
occupations= 'smearing', smearing = 'm-p', degauss = 0.1
/
&ELECTRONS
mixing_beta = 0.00075
conv_thr = 1.0d-8
electron_maxstep = 70
/
&IONS
/
&CELL
/
ATOMIC_SPECIES
C 12.011 C.pbesol-n-rrkjus_ps1.1.0.0.UPF
N 14.007 N.pbesol-n-rrkjus_ps1.1.0.0.UPF
H 1.008 H.pbesol-rrkjus_ps1.0.1.UPF
Pb 207.2 Pb.pbesol-dn-rrkjus_ps1.1.0.0.UPF
I 126.90 I.pbesol-n-rrkjus_ps1.1.0.0.UPF
CELL_PARAMETERS angstrom
6.28880000 0.00000000 0.00000000
0.00154263 6.22876981 0.00000000
0.13973295 -0.00036613 6.37255819
ATOMIC_POSITIONS angstrom
C 5.68762816 6.22746232 2.91755469
N 0.76248596 -0.00015695 3.49068983
H 5.76522586 6.22643528 1.82113056
H 5.15723272 0.90114080 3.25657478
H 5.15968675 5.32511200 3.25829538
H 1.30458379 0.84536565 3.19592078
H 1.30663813 5.38278144 3.19763499
H 0.76813187 0.00090438 4.53227809
Pb 2.93516392 3.11390239 6.22995946
I 2.64234654 3.11409882 3.02788916
I 2.51578467 6.22849954 0.15080022
I 5.99299067 3.11401602 5.87855111
K_POINTS automatic
4 4 4 0 0 0
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