[Wien] hyperfine field question in ORB package for the aluminum
Jing-Han Chen
jhchen at tamu.edu
Tue Oct 15 18:25:57 CEST 2013
Dear Prof. Blaha and other wien2k users:
(I posted a similar message yesterday, apologies in case this appears as a
repeat; the first message has not appeared on the list, perhaps reflected
due to included images.)
Regarding tests of the hyperfine fields in aluminum metal, we had thought
about the issue of insufficient k-points, however we thought we had a
handle on this issue. In a 9 T field, a rough calculation shows that the
thin spin-polarized shell at Ef represents about 1/3000 of the BZ volume
for fcc-Al. We ran a script gradually increasing the number of k-points,
with a result (shown in http://people.physics.tamu.edu/jhchen/points.png)
that the HFF settles down within about 20% of the expected value for 10,000
k-points in B=9T, with fluctuations dying down to the order of 10% and less
in the range 30,000 - 80,000 k-points. We also ran a test for linearity in
B at a setting of 10,000 k-points, and the results appeared to be quite
linear up to 100 T (shown in http://people.physics.tamu.edu/jhchen/field.png
).
We ran the test treating fcc-Al as simple cubic with 4 sites in order to be
sure we understood how the field is applied in ORB, and expected if
anything better convergence since the expanded cell gives a greater k-point
density. However the results seem strange: with several k-point settings we
found that in general, the HFF approached the expected value for fcc-Al
after a relatively small number of iterations, yet without quite
converging, and finally the HFF values diverged, with one or more going
large and negative. We had not tried as many variations as for fcc since
the results are much slower to obtain converged HFF.
Following the suggestion of Prof. Blaha after our last posting we tried
increasing to very large field and k-point values, and did finally get
convergence (more than 10 last iterations of HFF is the same) for a setting
of 100000 k-points and 10000 T, yielding 4 reasonably close positive
values as in the following:
------
:HFF001: 143.345 0.000 0.572 143.917
(KGAUSS)
:HFF002: 143.344 0.000 0.572 143.916
(KGAUSS)
:HFF003: 144.427 0.000 0.583 145.010
(KGAUSS)
:HFF004: 143.344 0.000 0.572 143.916
(KGAUSS)
------
However we are concerned that the HFF values are still not identical,
whereas at 10,000 T the spin-polarized shell at Ef represents a significant
fraction of the BZ, and the spin energy is quite large. We expected this to
be more than enough k-points for random sampling of the shell at Ef. For
this reason, and in particular in light of the strange behavior in which
the HFF values almost converge before diverging to widely separated values,
is it possible that there might be some other issue that we are overlooking?
Any suggestions would be appreciated.
2013/10/7 Peter Blaha <pblaha at theochem.tuwien.ac.at>
> The hyperfine field for a metal is coming mainly from the contact term due
> to the induced spin-polarization by the magnetic field.
>
> You should notice, that a field of 9 T is (for theoretical calculations)
> an extremely small field, causing a very small spin-splitting of the states
> near EF, which causes the HFF.
> I suppose all you see is numerical noise.
>
> Since only the states at EF are of interest (the field can only reoccupy
> states within a few mRy (or less) around EF), you need to converge your
> calculation with respect to:
>
> a) the k-mesh (test MUCH larger meshes (10000, 50000 100000 k or more)
> b) the magnetic field (increase it and test fields up to 1000 T), You are
> not interested in the absolute number, but in ppm, i.e. the relative
> induced field.
>
> c) The angular momentum component of the hFF introduced by case.vorbup/dn
> is NOT correct. I would even suggest that you put l=0 to
> minimize the effect (or use -orbc with case.vorbup/dn , where all
> elements are set to zero.)
>
> d) In principle the orbital contribution should be obtainable from the
> NMR-module of wien2k_13. However, also there we observed for metals that it
> is very hard to converge with respect to k-mesh and the final results (sum
> of spin and orbital contribution) does not seem right, while spin-only has
> the correct magnitude (within 10% of the experiment). This is an unresolved
> issue for us so far.
>
>
> Am 07.10.2013 04:01, schrieb Jing-Han Chen:
>
>> Dear WIEN2k users and authors
>>
>> We are currently working on the hyperfine field calculation by using
>> ORB package. In fcc aluminum case, we got 0.154 (KGAUSS) when the
>> following case.inorb and case.indm are used
>>
>> case.inorb
>> 3 1 0 nmod, natorb, ipr
>> PRATT, 1.0 mixmod, amix
>> 1 1 0 iatom nlorb, lorb
>> 9. Bext in T
>> 0. 0. 1. direction of Bext in terms of lattice vectors
>>
>> case.indm
>> -9. Emin cutoff energy
>> 1 number of atoms for which density matrix is
>> calculated
>> 1 1 0 index of 1st atom, number of L's, L1
>> 0 0 r-index, (l,s)index
>>
>> In order to confirm how the magnetic field is applied for the
>> multiple sites crystal, we made aluminum as a simple cubic with 4
>> inequivalent sites and we believe it should be physically identical to
>> fcc. The following case.inorb and case.indm are used.
>>
>> case.inorb
>> 3 4 0 nmod, natorb, ipr
>> PRATT, 1.0 mixmod, amix
>> 1 1 0 iatom nlorb, lorb
>> 2 1 0 iatom nlorb, lorb
>> 3 1 0 iatom nlorb, lorb
>> 4 1 0 iatom nlorb, lorb
>> 9. Bext in T
>> 0. 0. 1. direction of Bext in terms of lattice vectors
>>
>> case.indm
>> -9. Emin cutoff energy
>> 4 number of atoms for which density matrix is
>> calculated
>> 1 1 0 index of 1st atom, number of L's, L1
>> 2 1 0 index of 1st atom, number of L's, L1
>> 3 1 0 index of 1st atom, number of L's, L1
>> 4 1 0 index of 1st atom, number of L's, L1
>> 0 0 r-index, (l,s)index
>>
>> Both fcc and simple cubic are run by the same way (-orb -cc 0.00001).
>> A complete different HFFs are obtained as the following
>>
>> :HFF001: 0.059 0.000 0.001
>> 0.060 (KGAUSS)
>> :HFF002: -1.193 0.000 -0.010
>> -1.204 (KGAUSS)
>> :HFF003: 1.681 0.000 0.011
>> 1.692 (KGAUSS)
>> :HFF004: 0.046 0.000 0.001
>> 0.047 (KGAUSS)
>>
>> We got four different HFFs which we thought they are supposed to be the
>> same. Also all of them are very far from the fcc result (0.154 KGAUSS).
>> Does anyone know why it happens?
>>
>> Any suggestion and comment are appreciated.
>>
>> --
>> Jing-Han Chen
>> Graduate Student
>> Department of Physics
>> Texas A&M University
>> 4242 TAMU
>> College Station TX 77843-4242
>> jhchen at tamu.edu <mailto:jhchen at tamu.edu> <jhchen at tamu.edu
>> <mailto:jhchen at tamu.edu>> / http://people.physics.tamu.**edu/jhchen/<http://people.physics.tamu.edu/jhchen/>
>>
>>
>>
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>>
> --
> Peter Blaha
> Inst.Materials Chemistry
> TU Vienna
> Getreidemarkt 9
> A-1060 Vienna
> Austria
> +43-1-5880115671
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--
Jing-Han Chen
Graduate Student
Department of Physics
Texas A&M University
4242 TAMU
College Station TX 77843-4242
jhchen at tamu.edu <jhchen at tamu.edu> / http://people.physics.tamu.edu/jhchen/
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