[ase-users] magnetic moments

[Carsten Rostgaard]

No, they are written / read correctly, but a few weird things happen. 
Consider the follwing

from ase import *
from gpaw import *

calc = GPAW()
atoms = molecule('CH', calculator=calc, cell=[5, 6, 7])
atoms.center()
atoms.get_potential_energy()

print atoms.get_magnetic_moment() # 1
print atoms.get_magnetic_moments() # array([ 1.01433322, -0.01433322])
print atoms.get_initial_magnetic_moments() # array([ 1.,  0.])

calc.write('test.gpw')

atoms, calc = restart('test.gpw')
print atoms.get_magnetic_moment() # 0
print atoms.get_magnetic_moments() # array([ 1.01433322, -0.01433322])
print atoms.get_initial_magnetic_moments() # array([ 1.01433322, 
-0.01433322])

The commented values are the outputs.

As you see, the total magnetic moment is lost when writing a gpw file 
(this is a bug I reported back in May 2008 
https://trac.fysik.dtu.dk/projects/gpaw/ticket/43).

The second weird thing is that the initial magnetic moments property on 
the atoms gets changed to the calculated local magnetic moments after 
dumping to file. I think this is intentional though, as this will be a 
better starting guess if you restart a calculation.

Cheers,
Carsten


Vivien Petzold wrote:
> Dear ASE users,
>
> I have made some mysterious observations by doing the following:
>
> > from gpaw import restart
> > atoms, calc = restart(<myfile>)
>
> <myfile> is a gpw-file containing an originally spin-polarized 
> calculation of a Cl2 molecule. Both atoms had magmom=1 in the 
> calculation that generated myfile.
>
> > atoms.get_magnetic_moments()
> array([ 0.,  0.])
> > atoms[0]
> Atom('Cl', [6.0, 6.5, 8.007541], tag=0, magmom=0.0, index=0)
> > atoms[1]
> Atom('Cl', [6.0, 6.5, 5.992459], tag=0, magmom=0.0, index=1)
>
> The information of the initial magmoms is apparently lost. So, I am 
> setting them again:
>
> > atoms.set_magnetic_moments((1,1))
> > atoms.get_magnetic_moments()
> array([ 0.,  0.])
>
> Hmmm ...? But, interestingly
>
> > atoms[0]
> Atom('Cl', [6.0, 6.5, 8.007541], tag=0, magmom=1.0, index=0)
> > atoms[1]
> Atom('Cl', [6.0, 6.5, 5.992459], tag=0, magmom=1.0, index=1)
>
> What is going on? Are the magnetic moments set or not? And why are 
> they not stored in the gpw-file (a question that should rather go to 
> the gpaw mailing list)?
>
> Thanks for any help,
> Vivien
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-- 
Carsten Rostgaard
Ph.D. Student, M.Sc.Eng (Applied Physics)
CAMD, Department of Physics, Technical University of Denmark
Room 221, Building 307, DTU, DK-2800 Kongens Lyngby, Denmark
E-mail: Carsten.Rostgaard at fysik.dtu.dk - Phone: +45 4525 3185