[Wien] zigzag potential (remaining questions)
Peter Blaha
pblaha at theochem.tuwien.ac.at
Fri Jan 5 12:20:53 CET 2018
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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--
P.Blaha
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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: blaha at theochem.tuwien.ac.at WIEN2k: http://www.wien2k.at
WWW: http://www.imc.tuwien.ac.at/TC_Blaha
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