[Wien] zigzag potential (remaining questions)

[Stefaan Cottenier]

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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