[Pw_forum] big difference between "total magnetization" and "absolute magnetization" for 4f elements

[琨陶]

I try to force two Gd atom into ferromagnetic with following parameters:

    nat= 2, ntyp=2,
    starting_magnetization(1)=1.0,
    starting_magnetization(2)=1.0,

ATOMIC_SPECIES
 Gd1  1.0  Gd.GGA-PBE-paw.UPF
 Gd2  1.0  Gd.GGA-PBE-paw.UPF
ATOMIC_POSITIONS {crystal}
Gd1  0.33333333  0.66666667  0.25
Gd2  0.66666667  0.33333333  0.75

And I got the following results:

     total magnetization       =     7.55 Bohr mag/cell
     absolute magnetization    =     8.02 Bohr mag/cell

In this case, even the "absolute magnetization" is wrong. And the
magnetic moments on two atoms are 0.47, 7.08, respectively, which are
are away from the experimental results 7.8 for each atom.

I do not know the reason, perhaps there is a small bug in the code for
4f elements or due to some incorrect parameters in my input file. Any
suggestion is appreciated!

With regards,
Kun Tao

On 13 March 2013 12:35, mohnish pandey <mohnish.iitk at gmail.com> wrote:
> Did you try using different initial spin configurations? If your interested
> in FM ground state then may be you should try initial magnetic configuration
> as FM. e.g. +1, +1 for both.
>
>
> On Wed, Mar 13, 2013 at 9:03 PM, 琨陶 <taokun76 at gmail.com> wrote:
>>
>> Thank you for your suggestions. When I set two atoms in the unit cell
>> to be antiferromagnetic, the "total magnetization" is nearly zero, and
>> the "absolute magnetization" is about 14.67. And the magnetic moment
>> for two atoms are about 7.16 and -7.18, which is more or less
>> acceptable.
>>
>> Now, the question is that why "total magnetization" and "absolute
>> magnetization" differs so much if I want to force two atoms into a
>> ferromagnetic configuration.
>>
>> Any suggestions? Thanks!
>>
>> With regards,
>> Kun Tao
>>
>>
>> On 13 March 2013 11:14, Andrei Malashevich <andrei.malashevich at yale.edu>
>> wrote:
>> > If you want to model antiferromagnetic structure, you should define two
>> > types of atoms, Gd1 and Gd2.
>> > Change ntyp to 2. Use, e.g.,
>> >  starting_magnetization(1)=1.0
>> > starting_magnetization(2)=-1.0
>> >
>> > ATOMIC_SPECIES
>> >  Gd1  1.0  Gd.GGA-PBE-paw.UPF
>> >  Gd2  1.0  Gd.GGA-PBE-paw.UPF
>> > ATOMIC_POSITIONS {crystal}
>> > Gd1  0.33333333  0.66666667  0.25
>> > Gd2 0.66666667  0.33333333  0.75
>> >
>> >
>> > On Wed, Mar 13, 2013 at 11:05 AM, 琨陶 <taokun76 at gmail.com> wrote:
>> >>
>> >> Hi,
>> >>
>> >> Yes, the bulk Gd without Hubbard U is antiferromagnetic. If I set the
>> >> two atoms in the unit cell to be antiferromagnetic, the "total
>> >> magnetization" should be equal to zero, and the "absolute
>> >> magnetization" is what I have gotten. Now, however, the "total
>> >> magnetization" is not zero. Could you give me some suggestions?
>> >> Thanks!
>> >>
>> >> With regards,
>> >> Kun Tao
>> >>
>> >> On 13 March 2013 10:48, Stefano de Gironcoli <degironc at sissa.it> wrote:
>> >> > are you sure you are defining the correct magnetic structure ?
>> >> > is Gd maybe antiferromagnetic ?
>> >> > stefano
>> >> >
>> >> > On 03/13/2013 03:19 PM, 琨陶 wrote:
>> >> >> Dear everyone,
>> >> >>
>> >> >> I want to calculate the magnetic properties of bulk Gd whose
>> >> >> magnetic
>> >> >> moment is about 8 Bohr magneto/atom. Usually, in the output file
>> >> >> values of "total magnetization" and "absolute magnetization" should
>> >> >> be
>> >> >> nearly the same. However, in my output file, I found a big
>> >> >> difference
>> >> >> between them as following:
>> >> >>
>> >> >>       total magnetization       =     8.00 Bohr mag/cell
>> >> >>       absolute magnetization    =    15.72 Bohr mag/cell
>> >> >>
>> >> >> The good news is that the "absolute magnetization" is close to the
>> >> >> experimental results (7.86 Bohr mag/atom), the bad news is that the
>> >> >> "total magnetization" is wrong. Moreover, when I try to calculate
>> >> >> the
>> >> >> magnetic moment on each atom with projwfc.x program, I got about 4.1
>> >> >> Bohr mag/atom.
>> >> >>
>> >> >> Could you give me some suggestions? Any advice are appreciated,
>> >> >> thanks!
>> >> >>
>> >> >> Regards,
>> >> >> Kun Tao
>> >> >>
>> >> >>
>> >> >> Attached below is the input file:
>> >> >>
>> >> >>   &control
>> >> >>      calculation='scf'
>> >> >>      restart_mode='from_scratch',
>> >> >>      prefix='Gd',
>> >> >>      pseudo_dir = './'
>> >> >>      outdir='./',
>> >> >>   /
>> >> >>   &system
>> >> >>      ibrav= 4, celldm(1)= 6.96, celldm(3)= 1.59,
>> >> >>      nat= 2, ntyp=1,
>> >> >>      nspin = 2,
>> >> >>      starting_magnetization(1)=1.0,
>> >> >>      ecutwfc=55.0,
>> >> >>      ecutrho=220.0,
>> >> >>      occupations ='smearing',
>> >> >>      smearing ='gauss',
>> >> >>      degauss = 0.01,
>> >> >>   /
>> >> >>   &electrons
>> >> >>      diagonalization='david',
>> >> >>      mixing_beta = 0.3,
>> >> >>      conv_thr = 1.0d-8,
>> >> >>   /
>> >> >> ATOMIC_SPECIES
>> >> >>   Gd  1.0  Gd.GGA-PBE-paw.UPF
>> >> >> ATOMIC_POSITIONS {crystal}
>> >> >> Gd  0.33333333  0.66666667  0.25
>> >> >> Gd  0.66666667  0.33333333  0.75
>> >> >> K_POINTS {automatic}
>> >> >> 4 4 4 0 0 0
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>
>
> --
> Regards,
> MOHNISH,
> -----------------------------------------------------------------
> Mohnish Pandey,
> PhD Student,
> Center for Atomic Scale Materials Design,
> Department of Physics,
> Technical University of Denmark
> -----------------------------------------------------------------
>
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