[ase-users] magnetic moments

[Jens Jørgen Mortensen]

On Fri, 2009-01-16 at 11:34 +0100, Carsten Rostgaard wrote:
> Ahh... I forgot one point.
> 
> To clarify:
> atoms.get_magnetic_moments() returns the calculated local magnetic moments
> atoms.get_initial_magnetic_moments() returns the value of magmoms, set 
> in the constructor of the Atoms class
> 
> But:
> atoms.set_magnetic_moments() Set the *initial* magnetic moments, i.e. 
> the Atoms attribute, which does not depend on the calculation.
> 
> Maybe we should rename the latter to atoms.set_initial_magnetic_moments() ?

That's a good idea.  Done:

  https://trac.fysik.dtu.dk/projects/ase/changeset/757

> ps. this explains why
> atoms.set_magnetic_moments(1)
> print atoms.get_magnetic_moments()
> does not give the same value.
> 
> Carsten Rostgaard wrote:
> > 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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> >> ase-users at listserv.fysik.dtu.dk
> >> https://listserv.fysik.dtu.dk/mailman/listinfo/ase-users
> >
>