Besides the remark by L.Marks, that you can get more info by putting
-999 for IFIELD,
I can only recommend to put R2V in case.in0 and plot the resulting
potentials with a field. (Best is a 1D plot along z, preferentially not
through any atoms.) You should clearly see where the kinks are, and also
how large delta-V / delta-l really is (plot in Ry units in in5).
In that way you can verify if the statement in the UG is correct or not.
PS: I'll take up any "explicit" suggestion for the UG. (but not just
"please improve it").
Best regards
Peter
On 01/05/2018 09:55 AM, Stefaan Cottenier wrote:
With my interpretation problem being solved (see previous summarizing
mail), I’m left with the two questions about the value and “phase” of
the zigzag potentials. For clarity, I repeat here these two questions
(copied from the initial post).
Thanks,
Stefaan
================
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)
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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--------------------------------------------------------------------------
Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-165300 FAX: +43-1-58801-165982
Email: bl...@theochem.tuwien.ac.at WIEN2k: http://www.wien2k.at
WWW: http://www.imc.tuwien.ac.at/TC_Blaha
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