[Pw_forum] question on constraint magnetic moment calculation

[Pang Rui]

Yes and No.
If one just changes the target amplitude and recalculates, the constraint
energy will change little, and the magnetic moment will get reduced.
But if one switches to constrained_magnetization="atomic direction"(give
up constraining on amplitude) and restart from the file, the constraint
energy will get reduced to the order of 0.01Ry, however cannot go smaller.
I think it is still a little large to be used in calculating magnetic
coupling constants, isn`t it? So do you have any suggestion?   
On Fri, 4 Jul 2014 16:56:04 +0200, Gabriele Sclauzero
<gabriele.sclauzero at mat.ethz.ch> wrote:
> OK, but here you are showing a different case where you fix the local 
> magnetic moment (as a vector)...
> 
> In this case, for some reason the local moment along z is still a bit 
> far from the target of 2.8, therefore the penalty energy is still large 
> (also given the large value of the lambda prefactor). Does it work with 
> a smaller constrained moment, say 2.5?
> 
> GS
> 
> On 07/04/2014 04:31 PM, Pang Rui wrote:
>> Dear Gabriele Sclauzero:
>> I covered the output, so I gave a new one with the same problems.The
>> input
>> file can be seen in the end. The only difference is the angle and
>> amplitude. The scf converged after 59 steps(In default conv_thr). The
>> output of the magnetic moment is as followed
>>
>>
==============================================================================
>>       atom number    1 relative position :    0.3750   0.0000   0.0000
>>       charge :    13.367288
>>       magnetization :          0.000122    0.000076    2.717489
>>       magnetization/charge:    0.000009    0.000006    0.203294
>>       polar coord.: r, theta, phi [deg] :     2.717489    0.003039
>> 31.837662
>>       constrained moment :     0.000000    0.000000    2.800000
>>
>>
>>
==============================================================================
>>
>>
>>
==============================================================================
>>       atom number    2 relative position :    0.6250   0.0000   0.0000
>>       charge :    13.367507
>>       magnetization :          0.000165    0.000174    2.717217
>>       magnetization/charge:    0.000012    0.000013    0.203270
>>       polar coord.: r, theta, phi [deg] :     2.717217    0.005053
>> 46.399234
>>       constrained moment :     0.000000    0.000000    2.800000
>>
>>
>>
==============================================================================
>> But the constraint energy (Ryd) = 2.04918119.
>> The question is, the lambda has been quite large, scf problems will
occur
>> if it is increased. But the constraint energy is still large. How can I
>> get
>> both constraint energy and scf converged in a constraint magnetic
moment
>> calculation?
>> Thanks for the reply.
>>   
>> INPUTFILE:
>>   &control
>>      pseudo_dir = "~/pr/QE5/pseudo"
>>      outdir="./",
>>      calculation="scf",
>>   /
>>   &system
>>      ibrav=  0, nat=  2, ntyp= 2,
>>      ecutwfc = 280.0,
>>      occupations='smearing',
>>      degauss=0.001,
>>      smearing='gauss'
>>      starting_magnetization(1)=2.8
>>      starting_magnetization(2)=2.8
>>      angle1(1)=0.0
>>      angle1(2)=0.0
>>      angle2(1)=0.0
>>      angle2(2)=0.0
>>      constrained_magnetization="atomic"
>>      noncolin=.ture.
>>      lambda=150.0
>>      nosym=.true.
>> /
>>   &electrons
>>      mixing_beta = 0.1
>>      electron_maxstep=200
>>   /
>> ATOMIC_SPECIES
>> Fe1 56 Fe.pbe-sp-hgh.UPF
>> Fe2 56 Fe.pbe-sp-hgh.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

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