[Pw_forum] Convergence problem with Pb180Se180 Cluster optimization

[ashkan shekaari]

Dear Naren,
Increase ecut. Use more intense kpoint mesh.

On Apr 21, 2017 4:50 PM, "Giuseppe Mattioli" <giuseppe.mattioli at ism.cnr.it>
wrote:

>
> Dear Naren
> Your calculation is very expensive, and calculations of 0D objects in a
> plane-wave/PBC framework are often prone to convergence issues. This said,
> you
> can try to
>
> 1) perform a simple calculation of the PbSe unit cell with the same
> pseudopotentials. Are there similar convergence problems? You are using hgh
> that
> are norm-conserving pseudopotentials (NCPP) and they could require a
> richer pw basis set. I would not be surprised if, after proper convergence
> tests
> performed on the unit cell, you ended up with ecutwfc=70~80 Ry. There is
> no need to specify ecutrho, anyway. It is fixed to a default ecutwfc*4 value
> in the case of NCPP.
>
> 2) lower mixing_beta, even down to very small values such as 0.05~0.01.
> Sometimes it helps to reach convergence (slowly but steady).
>
> It is impossible to say more without looking at you cluster, but if it is
> simply cut out from the bulk along low-index directions (e.g., a cube) you
> have to deal with a mess of surface dangling bonds that want to play nasty
> charge displacements between occupied and unoccupied electronic levels,
> even inducing a metallic character in your cluster. People used to
> saturate such dangling bonds with pseudo-H atoms (H atoms having formal
> charge
> lower or higher than 1.0, depending on the formal valence of the saturated
> atom). If you don't want to saturate the surface you must keep into account
> the possibility that the cluster surface reconstruct, and you should
> anticipate reconstruction trends by lplacing the atoms nearer to the
> expected
> final positions. It could be a very difficult task, look at the
> instructive story of the Si 7x7 reconstruction in this movie!
>
> https://www.youtube.com/watch?v=BXdC0NhAMBY
>
> HTH
> Giuseppe
>
> On Friday, April 21, 2017 04:06:06 AM Narendranath Ghosh wrote:
> > Dear all!
> >
> >
> >
> > I am currently trying to optimizing a Pb180Se180 cluster using  QE.
> >
> > But after 83 iterations it didn’t get converged.
> >
> > *Input  *
> >
> > calculation='relax',
> >
> >   outdir='/staging/op/NAREN_USC/PbSe_360_FINAL_based_Pb68Se68/OUTPUT',
> >
> >   prefix='PbSe-360',
> >
> >   pseudo_dir='/staging/op/NAREN_USC/PbSe_360_FINAL_based_
> Pb68Se68/pseudo',
> >
> >   verbosity='low',
> >
> > /
> >
> >
> >
> > &SYSTEM
> >
> >   ibrav=0,
> >
> >   celldm(1)=90.7068539791d0,
> >
> >   nat=360,
> >
> >   ntyp=2,
> >
> >   ecutwfc=30.0d0,
> >
> >   ecutrho=120.0d0,
> >
> >   input_dft='PBE',
> >
> >   occupations='smearing',
> >
> >   smearing='gaussian',
> >
> >   degauss=0.002000d0,
> >
> > /
> >
> > &ELECTRONS
> >
> >   diagonalization='david',
> >
> >   mixing_mode='plain',
> >
> >   mixing_beta=0.700d0,
> >
> > /
> >
> > &IONS
> >
> > /
> >
> > ATOMIC_SPECIES
> >
> >  Pb 207.200000d0 Pb.pbe-hgh.UPF
> >
> >  Se 78.960000d0  Se.pbe-hgh.UPF
> >
> >
> >
> > ATOMIC_POSITIONS {alat}
> >
> >   Pb   0.4831100000d0   0.4740500000d0   0.4999300000d0
> >
> >   Se   0.5190800000d0   0.5278700000d0   0.5981100000d0
> >
> >   Se   0.5901900000d0   0.4712600000d0   0.2154800000d0
> >
> > ……………………………………………………
> ………….
> >
> > K_POINTS {gamma}
> >
> >
> >
> > CELL_PARAMETERS {alat}
> >
> >   1.000000000000d0  0.000000000000d0  0.000000000000d0
> >
> >   0.000000000000d0  1.000000000000d0  0.000000000000d0
> >
> >   0.000000000000d0  0.000000000000d0  1.000000000000d0
> >
> >
> >
> >
> >
> > *Output*
> >
> >     iteration # 81     ecut=    30.00 Ry     beta=0.70
> >
> >      Davidson diagonalization with overlap
> >
> >      WARNING:     9 eigenvalues not converged in regterg
> >
> >      ethr =  4.62E-04,  avg # of iterations = 21.0
> >
> >
> >
> >      total cpu time spent up to now is    92680.3 secs
> >
> >
> >
> >      total energy              =    2098.58547221 Ry
> >
> >      Harris-Foulkes estimate   =  -16225.87153481 Ry
> >
> >      estimated scf accuracy    <  209398.02191142 Ry
> >
> >
> >
> >      iteration # 82     ecut=    30.00 Ry     beta=0.70
> >
> >      Davidson diagonalization with overlap
> >
> >      WARNING:     5 eigenvalues not converged in regterg
> >
> >      c_bands:  5 eigenvalues not converged
> >
> >      ethr =  4.62E-04,  avg # of iterations = 20.0
> >
> >
> >
> >      total cpu time spent up to now is    95793.4 secs
> >
> >
> >
> >      total energy              =    1914.32044477 Ry
> >
> >      Harris-Foulkes estimate   =  -18801.41916562 Ry
> >
> >      estimated scf accuracy    <  243341.55571758 Ry
> >
> >
> >
> >      iteration # 83     ecut=    30.00 Ry     beta=0.70
> >
> >      Davidson diagonalization with overlap
> >
> >      WARNING:   138 eigenvalues not converged in regterg
> >
> >      ethr =  4.62E-04,  avg # of iterations = 27.0
> >
> >
> >
> >      total cpu time spent up to now is    99442.6 secs
> >
> >
> >
> >      total energy              =    1659.36438352 Ry
> >
> >      Harris-Foulkes estimate   =  -15989.48139862 Ry
> >
> >      estimated scf accuracy    <  138246.99363207 Ry
> >
> >
> >
> > Any comment to help me getting started is very much appreciated!
> >
> >
> >
> > Best regards,
> >
> > Naren
> >
> >
> >
> >
> >
> >
> >
> > *Dr. Narendra Nath Ghosh*
> >
> > *Research Associate*
> >
> > *University of Gour Banga*
> >
> > *Department of Chemistry*
> >
> > *Malda-732102*
> >
> > *India*
> >
> > *Phone: +919126667601*
>
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>
>    Giuseppe Mattioli
>    CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
>    v. Salaria Km 29,300 - C.P. 10
>    I 00015 - Monterotondo Stazione (RM), Italy
>    Tel + 39 06 90672342 - Fax +39 06 90672316
>    E-mail: <giuseppe.mattioli at ism.cnr.it>
>    http://www.ism.cnr.it/en/staff/giuseppe-mattioli/
>    ResearcherID: F-6308-2012
>
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