[Wien] zigzag potential interpretation
Xavier Rocquefelte
xavier.rocquefelte at univ-rennes1.fr
Tue Jan 2 15:44:46 CET 2018
To be honest I also feel that something is missing in my last arguments.
What is the electronic configuration of Fe at the surface? The orbital
occupancy could play a role in the understanding of the present
observation.
Le 02/01/2018 à 15:37, Xavier Rocquefelte a écrit :
>
> 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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>
>
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