[Wien] zigzag potential interpretation
Xavier Rocquefelte
xavier.rocquefelte at univ-rennes1.fr
Tue Jan 2 15:37:58 CET 2018
Dear Stefaan
As always it is very nice to read your posts :)
I will only react on your "Thought 3". What will happen if you do the
same calculation along 00-1? To my point of view, you will obtain the
same result. Indeed, the magnetic anisotropy (MAE) of bulk-Fe must be
symmetric. Here you break the symmetry, it could be seen considering 2
local pictures (for each slab surface):
- one experiencing a magnetization direction along 001
- one along 00-1.
These two directions must lead to the same SO effects and thus the same
spin moments, orbital moments and EFG.
Here is one plausible interpretation ;) I hope it will help you.
I wish you all the best and HAPPY NEW YEAR to you and your familly.
Xavier
Le 02/01/2018 à 14:33, Stefaan Cottenier a écrit :
>
> Dear wien2k mailing list,
>
> I know that the Berry phase approach is the recommended way nowadays
> for applying an external electric field in wien2k. However, for a
> quick test I resorted to the old zigzag potential that is described in
> the usersguide, sec. 7.1.
>
> It works, but I have some questions to convince me that I’m
> interpreting it the right way.
>
> The test situation I try to reproduce is from this paper
> (https://doi.org/10.1103/PhysRevLett.101.137201), in particular this
> picture
> (https://journals.aps.org/prl/article/10.1103/PhysRevLett.101.137201/figures/1/medium).
> It’s a free-standing slab of bcc-Fe layers, with an electric field
> perpendicular to the slab. For convenience, I use only 7 Fe-monolayers
> (case.struct is pasted underneath). Spin orbit coupling is used, and
> the Fe spin moments point in the positive z-direction.
>
> This is the input I used in case.in0 (the last line triggers the
> electric field) :
>
> TOT XC_PBE (XC_LDA,XC_PBESOL,XC_WC,XC_MBJ,XC_REVTPSS)
>
> NR2V IFFT (R2V)
>
> 30 30 360 2.00 1 min IFFT-parameters, enhancement factor,
> iprint
>
> 30 1.266176 1.
>
> Question 1: The usersguide tells “The electric field (in Ry/bohr)
> corresponds to EFIELD/c, where c is your c lattice parameter.” In my
> example, EFIELD=1.266176 and c=65.082193 b, hence the electric field
> should be 0.019455 Ry/bohr. That’s 0.5 V/Angstrom. However, by
> comparing the dependence of the moment on the field with the paper
> cited above, it looks like that value for field is just half of what
> it should be (=the moment changed as if it were subject to a field of
> 1.0 V/Angstrom). When looking at the definition of the atomic unit of
> electric field (https://physics.nist.gov/cgi-bin/cuu/Value?auefld), I
> see it is defined with Hartree, not Rydberg. This factor 2 would
> explain it. Does someone know whether 2*EFIELD/c is the proper way to
> get the value of the applied electric field in WIEN2k?
>
> Question 2: It is not clear from the userguide where the extrema in
> the zigzagpotential are. Are they at z=0 and z=0.5, as in fig. 6 of
> http://dx.doi.org/10.1103/PhysRevB.63.165205 ? I assumed so, that’s
> why the slab in my case struct is positioned around z=0.25. Adding
> this information to the usersguide or to the documentation in the code
> would be useful. (or alternatively, printing the zigzag potential as
> function of z by default would help too)
>
> Thought 3: This is not related to the electric field as such, but when
> playing with the slab underneath, I notice that in the absence of an
> electric field all properties of atoms 1 and 2 – the ‘left’ and
> ‘right’ terminating slab surfaces – are identical. Same spin moment,
> same orbital moment, same EFG,… I didn’t expect this, as with
> magnetism and spin-orbit coupling along 001, the magnetic moments of
> the atoms are pointing in the positive z-direction. That means ‘from
> the vacuum to the bulk’ for atom 1, and ‘from the bulk to the vacuum’
> for atom 2. That’s not the same situation, so why does it lead to
> exactly the same properties? What do I miss here? (The forces (:FGL)
> for atoms 1 and 2 are opposite, as expected. And when the electric
> field is switched on, atoms 1 and 2 do become different, as expected.)
>
> Thanks for your insight,
>
> Stefaan
>
> blebleble s-o calc. M|| 0.00 0.00 1.00
>
> P 7 99 P
>
> RELA
>
> 5.423516 5.423516 65.082193 90.000000 90.000000 90.000000
>
> ATOM -1: X=0.00000000 Y=0.00000000 Z=0.12500000
>
> MULT= 1 ISPLIT=-2
>
> Fe1 NPT= 781 R0=.000050000 RMT= 2.22000 Z: 26.00000
>
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
>
> 0.0000000 1.0000000 0.0000000
>
> 0.0000000 0.0000000 1.0000000
>
> ATOM -2: X=0.00000000 Y=0.00000000 Z=0.37500000
>
> MULT= 1 ISPLIT=-2
>
> Fe2 NPT= 781 R0=.000050000 RMT= 2.22000 Z: 26.00000
>
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
>
> 0.0000000 1.0000000 0.0000000
>
> 0.0000000 0.0000000 1.0000000
>
> ATOM -3: X=0.00000000 Y=0.00000000 Z=0.20833333
>
> MULT= 1 ISPLIT=-2
>
> Fe3 NPT= 781 R0=.000050000 RMT= 2.22000 Z: 26.00000
>
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
>
> 0.0000000 1.0000000 0.0000000
>
> 0.0000000 0.0000000 1.0000000
>
> ATOM -4: X=0.00000000 Y=0.00000000 Z=0.29166667
>
> MULT= 1 ISPLIT=-2
>
> Fe4 NPT= 781 R0=.000050000 RMT= 2.22000 Z: 26.00000
>
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
>
> 0.0000000 1.0000000 0.0000000
>
> 0.0000000 0.0000000 1.0000000
>
> ATOM -5: X=0.50000000 Y=0.50000000 Z=0.16666667
>
> MULT= 1 ISPLIT=-2
>
> Fe5 NPT= 781 R0=.000050000 RMT= 2.22000 Z: 26.00000
>
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
>
> 0.0000000 1.0000000 0.0000000
>
> 0.0000000 0.0000000 1.0000000
>
> ATOM -6: X=0.50000000 Y=0.50000000 Z=0.33333333
>
> MULT= 1 ISPLIT=-2
>
> Fe6 NPT= 781 R0=.000050000 RMT= 2.22000 Z: 26.00000
>
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
>
> 0.0000000 1.0000000 0.0000000
>
> 0.0000000 0.0000000 1.0000000
>
> ATOM -7: X=0.50000000 Y=0.50000000 Z=0.25000000
>
> MULT= 1 ISPLIT=-2
>
> Fe7 NPT= 781 R0=.000050000 RMT= 2.22000 Z: 26.00000
>
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
>
> 0.0000000 1.0000000 0.0000000
>
> 0.0000000 0.0000000 1.0000000
>
> 8 NUMBER OF SYMMETRY OPERATIONS
>
>
>
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