[Pw_forum] fixed spin moment calculation

[Gabriele Sclauzero]

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 <mailto:E-Mail%3Ayuminqian at gmail.com>
> P.O.Box 603   Beijing 100190
> China
> 
> 
> ------------------------------------------------------------------------
> 
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum

-- 


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