[Pw_forum] question on constraint magnetic moment calculation

[Gabriele Sclauzero]

Dear Pang Rui,

     It's difficult to judge just from the input. Has the scf converged? 
What are the final values of theta for the two atoms? Can you report the 
relevant part of the output?

GS

On 06/28/2014 11:40 AM, Pang Rui wrote:
> Dear all
> Could anyone gave me some suggestion to do the constraint magnetic moment
> calculation?
> I followed the constraint magnetic moment calculation of the following
> handson with PWSCF.
> http://www.vasp.at/vasp-workshop/slides/handsonIV.pdf
> VASP uses the same method of PWSCF on constraint MM. However, I found the
> constraint energy is difficult to go zero. In the handson, they use
> lambda=50eV, got a constraint energy of 0.22591E-03eV. I used lambda=150Ry,
> but got a constraint energy=0.35Ry. Even PWSCF is different with VASP on
> some detail, I think it is not reasonable for two codes showing so large
> difference. So could anyone point the unreasonable part of my input file?
> Or give me some suggestion? This puzzled me for quite a long time.
> The following is the input file.
> &system
>      ibrav=  0, nat=  2, ntyp= 2,
>      ecutwfc = 80.0,
>      occupations='smearing',
>      degauss=0.001,
>      smearing='gauss'
>      starting_magnetization(1)=2.5
>      starting_magnetization(2)=2.5
>      angle1(1)=0.0
>      angle1(2)=45.0
>      angle2(1)=0.0
>      angle2(2)=90.0
>      constrained_magnetization="atomic direction"
>      noncolin=.ture.
>      lambda=150.0
>      nosym=.true.
> /
>   &electrons
>      mixing_beta = 0.1
>      electron_maxstep=200
>      startingwfc='file'
>      startingpot='file'
>   /
> ATOMIC_SPECIES
>   Fe1 56 Fe.pbe-spn-kjpaw_psl.0.2.1.UPF
>   Fe2 56 Fe.pbe-spn-kjpaw_psl.0.2.1.UPF
> ATOMIC_POSITIONS angstrom
> Fe1 3.0 0.0 0.0
> Fe2 5.0 0.0 0.0
> K_POINTS automatic
> 1 1 1 0 0 0
> CELL_PARAMETERS angstrom
>      8.0    0.0000000000000000    0.0000000000000000
>      0.0 8.0    0.0000000000000000
>      0.0 0.0 8.0
>
> PS1: I found the PWSCF used starting_magnetization as magnetization/charge
> for generating initial wave function,but used it as magnetization in
> constraint MM. So I set 2.5 for them.
> PS2: The startingwfc is of a smaller lambda calculation.


-- 
Dr. Gabriele Sclauzero
ETH Zurich
Materials Theory
HIT G 43.2
Wolfgang-Pauli-Str. 27
8093 Zürich, Switzerland

Phone +41 44 633 94 10
Fax +41 44 633 14 59
gabriele.sclauzero at mat.ethz.ch
http://www.theory.mat.ethz.ch/people/postdocs/gsclauze