[Pw_forum] fixed spin moment calculation

[yumin qian]

thanks for your reply ,I  changed the lambda=5.0 and used
   occupations='tetrahedra'  but the magnetization still did not converge to
the initial value ,but the total energy converged.
I do know what is the problem.
2009/3/11 Gabriele Sclauzero <sclauzer at sissa.it>

>
>
> yumin qian wrote:
> >   Dear PWSCF users
> >    I am doing calculate on the antiferromagnetic ground state of
> > LiNiO2, I want to plot the energy as a function of fixed spin moment  of
> > Ni atom.
> >   the following is my in put file for pwscf
> >
> >  &system
> >     ibrav = 0, nat=16 , ntyp= 4,
> >     ecutwfc = 35.0, ecutrho = 200.0,
> >     occupations='smearing', smearing='gaussian', degauss=0.02
>
> First of all a word of caution: this value of degauss may not be low enough
> to converge
> the magnetization (even if it is more than enough to converge the total
> energy). Also
> ecutrho may not be high enough to converge total energy, since you're using
> US PPs.
>
> >     nspin=2,constrained_magnetization='atomic',
> > starting_magnetization(1)= 0.0,
> > starting_magnetization(2)= 1.8,
> > starting_magnetization(3)=-1.8,
> > starting_magnetization(4)= 0.0,
> > lda_plus_u=.true.
> > Hubbard_U(1)=0.0
> > Hubbard_U(2)=3.0
> > Hubbard_U(3)=3.0
> > Hubbard_U(4)=0.0
> >   /
> >  &electrons
> >     diagonalization='david',
> >     conv_thr = 1.0e-6,
> >     mixing_beta = 0.5,
> >  /
> > ATOMIC_SPECIES
> > Li     *6.914*      Li.pbe-n-mt_bw.UPF
> > Ni1   *58.6934*    Ni.pbe-n-van.UPF
> > Ni2   *58.6934*    Ni.pbe-n-van.UPF
> > O   15.9994      O.pbe-van_bm.UPF
> >
> > and the output file gives
> >
> >
>  ==============================================================================
> >      atom number    5 relative position :   -0.1652   0.2839   0.5083
> >      charge :     2.373353
> >      magnetization :          1.544423
> >      magnetization/charge:    0.650735
> >      constrained moment :     1.800000
> >
> >
>  ==============================================================================
> > the output file gives a magnetic moment of 1.5444 ,how should I do to
> > make the calculation  converge to the starting_magnetization 1.8 ?
>
> You can increase the lambda parameter which premultiplies the penalty
> energy added in
> v_of_rho. In the limit your constraint gets satisfied, the energy should
> not depend on
> which lambda you chose, but you may want to verify this.
> The default should be 1. I think is not enough to force the magnetization
> on the atom.
>
> However, I think that the magnetization of a single atom inside a bulk
> material or in
> general when it forms covalent bonds is not a well defined quantity, so I
> would not care
> too much of the precise number I get for the magnetization, since it may
> well change if I
> change which portion of charge is attributed to which atom (remember that
> you're using a
> plane waves code, and PWs do not know anything about atomic orbitals a
> priori...)
>
> HTH
>
> GS
>
> >
> > I change the starting_magnetization(2) and starting_magnetization(3)
> > from 1.8 to 0.8 , then I will get the E(m) curve.  how should I do ,
> > does anyone give
> > a suggestion ?
> > --
> > Sincerely Y. M. Qian
> > Lab.of Condensed Matter Theory and Materials Computation
> > Institute of Physics
> > Chinese Academy of Sciences
> > Tel:  + 8610 8264 9147
> > E-Mail:yuminqian at gmail.com <E-Mail%3Ayuminqian at gmail.com> <mailto:
> E-Mail%3Ayuminqian at gmail.com <E-Mail%253Ayuminqian at gmail.com>>
> > P.O.Box 603   Beijing 100190
> > China
> >
> >
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> >
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>
> --
>
>
> o ------------------------------------------------ o
> | Gabriele Sclauzero, PhD Student                  |
> | c/o:   SISSA & CNR-INFM Democritos,              |
> |        via Beirut 2-4, 34014 Trieste (Italy)     |
> | email: sclauzer at sissa.it                         |
> | phone: +39 040 3787 511                          |
> | skype: gurlonotturno                             |
> o ------------------------------------------------ o
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-- 
Sincerely Y. M. Qian
Lab.of Condensed Matter Theory and Materials Computation
Institute of Physics
Chinese Academy of Sciences
Tel:  + 8610 8264 9147
E-Mail:yuminqian at gmail.com <E-Mail%3Ayuminqian at gmail.com>
P.O.Box 603   Beijing 100190
China
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