[gpaw-users] Problems with convergence under Constant Electric Field

[Jens Jørgen Mortensen]

Den 26-04-2016 kl. 19:50 skrev Rasmus Karlsson via gpaw-users:
> Dear Mikhail,
> have you considered using the davidson eigensolver instead? I should
> note that I haven't tried it with external fields. Nevertheless, it is much
> more simple to get convergence when using that eigensolver. I never use
> RMM-DIIS, because after all, a calculation that is finished tomorrow is
> still faster than one that quickly doesn't converge and fails at 3 am while
> you're in bed dreaming of the great results you'll get tomorrow. If the
> default eigensolver = 'dav' still doesn't work, consider importing the
> davidson and changing the options (see point 3 here:
> https://wiki.fysik.dtu.dk/gpaw/documentation/convergence.html)

You should also upgrade to version 1.0 of GPAW which has a new 
implementation of external potentials with correct forces:

     https://wiki.fysik.dtu.dk/gpaw/documentation/external.html

Jens Jørgen

> Rasmus
>
> Kuklin, Mikhail via gpaw-users writes:
>
>> Hello,
>>
>> I am trying to optimize 2D system with an applied electric field along z-direction by using gpaw.external_potential module. However, I encountered problems with convergence already with F=0.001 au. Does anyone can suggest me the way to solve this issue?
>>
>> Here is the script:
>>
>> ---
>> from ase.visualize import view
>> from ase.io import read
>> from ase.optimize import BFGS
>> from gpaw import GPAW, PW, FermiDirac
>> from gpaw.mixer import Mixer
>> from gpaw.eigensolvers import RMM_DIIS
>> from gpaw.external_potential import ConstantElectricField
>>
>> slab=read("test1.xyz")
>> a=4.80490
>> d=4.80490
>> slab.set_cell([a,a,d+15])
>> slab.center(axis=2)
>> slab.set_pbc([True, True, False])
>>
>> #view(slab)
>>
>> for h in [0.20]:
>>          calc=GPAW(
>>                  xc="PBE",
>>                  h=h,
>>                  kpts=(8,8,1),
>>                  spinpol=False,
>>                  mixer=Mixer(0.15, 10, 50),
>>                  occupations=FermiDirac(0.10),
>>                  eigensolver=RMM_DIIS(5),
>>                  external=ConstantElectricField(0.001, [0, 0, 1]),
>>                  txt="ml3_f2_opt.txt")
>>          slab.set_calculator(calc)
>>          slab.get_potential_energy()
>>          opt=BFGS(slab, trajectory="ml3_f2_opt.traj", maxstep=0.01, logfile="ml3_f2_opt.log")
>>          opt.run(fmax=0.025)
>>          calc.write("ml3_f2_opt.gpw”)
>> ---
>>
>> …and test1.xyz file in case if someone needs:
>>
>> ---
>> 12
>>
>> Ca       0.000000000      4.804903715      2.402450000
>> O        2.402449999      4.804903715      2.402450000
>> O        0.000000000      4.804903715      0.000000000
>> Ca       0.000000000      4.804903715     -2.402450000
>> O        2.402449999      4.804903715     -2.402450000
>> O       -0.000001858      2.402451858      2.402450000
>> Ca       2.402451858      2.402451858      2.402450000
>> Ca       2.402451858      4.804901857      0.000000000
>> O        2.402451858      2.402451858      0.000000000
>> Ca       2.402451858      2.402451858     -2.402450000
>> O        0.000001858      2.402451858     -2.402450000
>> Ca       0.000000000      2.402449999      0.000000000
>> —
>>
>> I tried to solve the problem by modifying mixer’s options and max step of BFGS, but it also did not help - forces are “walking” around the same value. It is worth to mention that under F=0.0001 convergence is fine.
>>
>> Thank you.
>>
>>
>> Best regards,
>>
>> Dr. Mikhail Kuklin
>> Postdoctoral researcher
>> Nanoscience center
>> Department of Physics
>> University of Jyväskylä
>> Finland
>>
>>
>>
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>