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

[Kuklin, Mikhail]

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