[Pw_forum] B_field

[孙阳]

Dear Gabriele and any other pwscf users:

Thank you for all of the informations. I do read the script of "add B_field",
one thing that makes me confused is that: the main structure of the
Program was written using conditional pattern, of which, I never find the
"i_cons == 5" case (which should be there, you can look it up in the
input.f90), which is, I guess, a core problem with my input.  In my "nspin=2"
calculation, there turns out a reminder in the output file: "i_cons
not programmed".
This is a reminder also in the "add_bfield.f90" to warn that "icons"
is out of range.

Actually, we just want to do a simple noncollinear calculation toward the
bulk Pd. We hope to use something may be more straightfowrd (just a hope).

The following is my input file:

****************************************************************************************

 &control
    calculation='scf'
    restart_mode='from_scratch',
    pseudo_dir = '$PSEUDO_DIR/',
    outdir='$TMP_DIR/'
    prefix='Pd'


 /
 &system
    ibrav = 2
    celldm(1) = 7.33361
    constrained_magnetization = 'total'
    nspin = 2
    fixed_magnetization(3) = 0.01
    ntyp = 1
    nat=1
    ecutwfc = 30.0
    ecutrho = 500.0
    occupations='tetrahedra'
    lambda=1
 /

 &electrons
    conv_thr = 1.0e-8
    mixing_beta = 0.1
 /
ATOMIC_SPECIES
 Pd  1.0  Pd.pz-nd-rrkjus.UPF

ATOMIC_POSITIONS
 Pd  0.0000 0.0000 0.000
K_POINTS (automatic)
 8 8 8 0 0 0
EOF
echo
echo "#######################################################################"
echo Running PW.x for the scf calculation ...
$PW_COMMAND < scf.in > scf.out
echo done

*****************************************************************************************

The report is:

 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
     from add_bfield : error #         1
     i_cons not programmed
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%


Overall, we just would like to add an B field to a bulk system. As
Gabriele pointed out that
the flag of "B_field(i)" might have been out of date. Any one has an
idea about this, your suggestion
is highly appreciated.

Thank you so much!!

Yang










2009/6/15 Gabriele Sclauzero <sclauzer at sissa.it>:
> Dear Yang (from???, please sign including your affiliation, since this is
> the "policy" of the PW forum),
>
> 孙阳 wrote:
>> Hi, Gabriele, I think you are right. I've already performed the
>> constrained magnetization
>> calculation. Would there be anyone introduce the way using
>> "constrained magnetizatio".
>> Is it fully equivalent to applying an external field?
>
> I'm not sure about this, but, since H (magnetic field) and M (magnetization) are
> conjugated variables, you can pass from one to the other as independent variable
> in the Hamiltonian via a Legendre transform. When you constrain the magnetization,
> the magnetic field will appear as a Lagrange multiplier, so if you use Lagrange
>  technique you get it automatically (see PRL 53,2512 about constrained DFT).
> In QE things are done in a different way, actually, and Lagrange multipliers are not
> used. If you fix the total magnetization in collinear LSDA, the "two Fermi energies"
> technique is used, while in the other cases a penalty functional is added (you have to
> tweak a bit with the "lambda" parameter: have a look at INPUT_PW and add_bfield.f90 for
> more detail).
> Anyway the code always gives you the "Hellman-Feynman" Magnetic field, H(M), as output at
> the end of the run. If you build the E(M) curve you should find, in principle, the same
> magnetic field by computing the derivative of E(M) w.r.t. M and thus get the same H(M) curve.
>
>
> HTH
>
> GS
>
>
>
>>
>> Thanks,
>>
>> Yang
>>
>> 2009/6/15 Gabriele Sclauzero <sclauzer at sissa.it>:
>>> It seems to me that B_field can be read from input, but then is not used in the
>>> calculation. Maybe it was an older option which has been replaced by another solution. In
>>> fact I think that a better way to see the effect of an external magnetic field is to do a
>>> calculation with constrained magnetization (see INPUT_PW for documentation): this should
>>> ensure to reach the ground states, while I suspect that applying a magnetic field you
>>> could end in a metastable state, depending on the starting conditions.
>>>
>>> Regards
>>>
>>> GS
>>>
>>> 孙阳 wrote:
>>>> Dear everyone:
>>>>
>>>> I try to appy an external magnetic field about 0.01 Ry to a bulk of
>>>> paramagnetic material. By either looking at the spin polarization and
>>>> the density of states, I could not find any polarization induced.
>>>> Any one has an idea. It will be highly appreciated!
>>>>
>>>> Yang
>>>>
>>> --
>>>
>>>
>>> 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
>>> _______________________________________________
>>> Pw_forum mailing list
>>> Pw_forum at pwscf.org
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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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