[Pw_forum] question on constraint magnetic moment calculation

[Pang Rui]

Dear Nguyen Chuong
It puzzled me for quite a long time. But I have checked the relation of
the output constraint energy and the output magnetic moment, and
experienced several calculations with QE5.0.2. It seemed that that when
the
starting magnetizations are interpreted as the target values of
magnetization moments in a constained calculation, they are in unit of
Bohr
not Bohr/e. And their meaning is magnetic moment rather than magnetic
moment over charge. "Values range of starting_magnetization at -1 (all
spin
down for the valence electrons of atom) to 1 (all spin-up)" is only true
when they are used to generate trial wave functions. You can check this by
run the inputfile. If I have misunderstandings, Please tell me.


On Fri, 4 Jul 2014 15:44:21 +0400, Nguyen Chuong
<chuongnguyen11 at gmail.com>
wrote:
> Dear Pang Rui,
> 
> starting_magnetization on atomic type i in a spin polarized calculation
> (such as nspin=2). Values range of starting_magnetization at -1 (all
spin
> down for the valence electrons of atom) to 1 (all spin-up).
> Following this link:
> 
>
http://www.quantum-espresso.org/wp-content/uploads/Doc/INPUT_PW.html#idp113952
> 
> 
> On Fri, Jul 4, 2014 at 3:36 PM, Gabriele Sclauzero <
> gabriele.sclauzero at mat.ethz.ch> wrote:
> 
>> 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
>>
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>>

-- 
PostDoc
Department of Physics, South University of Science and Technology of China