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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