[Wien] DOS plots for fixed spin moment LDA+U calculations
Peter Blaha
pblaha at theochem.tuwien.ac.at
Sat May 21 09:46:03 CEST 2016
In a normal runsp calculation, the sequence of program steps is:
x lapw1 -up # creates vectorup and energyup
x lapw1 -dn # vectordn energydn
x lapw2 -up # calculates EF from energy up/dn and clmvalup
x lapw2 -dn # clmvaldn
After an scf cycle, you thus still have "valid" enrgyup/dn and
vectorup/dn files, thus can run: x lapw2 -up/dn -qtl
in runfsm we have:
x lapw1 -up
cp energyup energydn !!!!
x lapw2 -up # with a larger NE in case.in2 file (cp in2up in2)
x lapw1 -dn
cp energydn energyup
x lapw2 -dn # with a smaller NE (cp case.in2dn case.in2)
This gives of course 2 different EF. Small correction of what L.Marks
said: It is true, that a FSM calculation does NOT give you a true fixed
point solution, except: you can interpret the difference in EF-up - dn
as a magnetic field, and thus the solution with a fixed moment of M=xx
is a solution with an magnetic field of delta-EF. (Note, in most of your
cases when far away from a scf-solution and without metamagnetic
transitions), the field would be unphysical and really huge (several
1000 Tesla).
From the above sequence it should now also be clear what you have to
for the qtls:
x lapw2 -dn -qtl is fine (since you still have the correct
energy/vector/in2 files .
x lapw1 -up
cp case.energyup case.energydn
cp case.in2up case.in2
x lapw2 -up -qtl
----------
For the DOS: x tetra -up/dn
Plotting the DOS in Ry is fine.
Plotting both up and dn DOS in eV in one plot is "wrong", since the
energy scale (0 eV = EF) corresponds to two different absolute energies
(EF) and thus one should shift up vs dn-DOS by delta-EF !!!!!!
Am 21.05.2016 um 06:35 schrieb Laurence Marks:
> I believe the problem here is that you have misunderstood the role of
> fixed spin moment calculations.
>
> In some cases there may be more than one fixed-point for a spin
> polarized calculator, i.e. two or more local minima with different
> spins. It can be useful to try and force a particular spin state, for
> instance to see if it is stable. The FSM code does this by controlling
> the relative number of up/dn electrons. For instance, with -m 8 there
> are always 8 more electrons in the up levels than the down, the Fermi
> level is not the same for the up/dn states.
>
> The FSM code only gets you close to a possible spin state, it does not
> yield a true fixed point. After doing the FSM calculation in all cases I
> can think of you need to remove the case.broyd* files and use runsp
> again. It may stabilize to a moment of 8, or it may not. You can't tell
> the electrons what to do!
>
> If you want to look at what the FSM calculation did, ignoring that it is
> not representative of anything, you have to do some tricks. Depending
> upon the current state of your directory you may have files case.in2up,
> case.in2dn and case.in2_fsm. The last one has the right number of
> valence electrons, similar to when you had when you did a straight runsp
> (and saved the results I hope). The in2up file will have 8 more, and
> in2dn 8 less. You will need to look at the csh script runfsm and see
> what it actually does for a normal lapw2, and then adapt this by hand
> adding -qtl. (I don't have the script handy.) I do not think there is a
> simple script in Wien2k to do this.
>
> ---
> Professor Laurence Marks
> "Research is to see what everybody else has seen, and to think what
> nobody else has thought", Albert Szent-Gyorgi
> http://www.numis.northwestern.edu
> Corrosion in 4D http://MURI4D.numis.northwestern.edu
> Partner of the CFW 100% gender equity project, www.cfw.org/100-percent
> <http://www.cfw.org/100-percent>
> Co-Editor, Acta Cryst A
>
>
> On May 20, 2016 22:46, "saurabh singh" <saurabhiitmandi at gmail.com
> <mailto:saurabhiitmandi at gmail.com>> wrote:
>
> Dear All users,
>
> Hope many people have faced similar problem in fixed spin moment DOS
> calculations
> I found problem in calculating DOS in fixed spin moment calculation.
> The similar question asked long before
> http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg00449.html
> but there is no answer given for that.
> In our case I do the LDA+U calculation I do follow the following
> step before calculating DOS
> 1. init_lapw
> 2.runsp_lapw -cc 0.0001
> 3. runsp_lapw -orb -cc 0.0001
> 4. runfsm_lapw -orb -m 8 -cc 0.0001
>
> I get total spin magnetic moment in unit cell 8.0001 μ_B. I do
> follow the instruction of user manual where it is recommended that
> one should run x lapw1 -orb -up before calculating the DOS. So i did
> it then i executed following command
> x lapw2 -qtl -up
> configure_init_lapw
> x tetra -up
>
> the above three command with dn. I calculated total DOS in present
> case. The problem I faced that
>
> 1. As per the manual "only case.vectordn is ok, but case.vectorup is
> NOT the proper up-spin vector and MUST NOT be used for the
> calculations of QTLs (and DOS). It must be regenerated by x lapw1
> -up ". Its ok then why if I calculate first the dos for dn spin and
> then follow the required correction of case.vectorup by running the
> x lapw1 -up command it gives two different fermi level in qtlup and
> qtldn file. This is done by the following steps :
> After SCF convergence
> x lapw2 -qtl -dn
> configure_init_lapw
> x tetra -dn
> x lapw1 -orb -up
> x lapw2 -qtl -up
> x tetra -up
>
> I also integrated DOS (case.dosevup/dn) for up and dn spin and found
> the difference in the integrated value at Fermi level (0 eV) is
> nearly 3.07. If the above steps is right it should be nearly 8
> 2. If I follow the following steps
> x lapw1 -orb -up
> x lapw2 -qtl -up
> configure_init_lapw
> x tetra -up
> x lapw2 -qtl -dn
> x tetra -dn
>
> Then I got same Fermi level in both the qtlup and qtldn file. But
> again the difference at Fermi level (i.e. 0 eV) in integrated value
> of up and down spin DOS is nearly 6.13, where as it should be nearly 8.
>
> I do not understand why this is happening. Can any one give the
> proper steps of finding the DOS for the fixed spin moment
> calculation. Where I am doing the mistakes or which procedure
> followed by me is wrong. I will be very grateful to you.
>
>
>
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--
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-165300 FAX: +43-1-58801-165982
Email: blaha at theochem.tuwien.ac.at WIEN2k: http://www.wien2k.at
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