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<p class="MsoNormal"><span lang="EN-US">Dear wien2k mailing list,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">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.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">It works, but I have some questions to convince me that I’m interpreting it the right way.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">The test situation I try to reproduce is from this paper (</span><span lang="EN-US" style="font-size:10.5pt;font-family:"Helvetica Neue";color:#222222;background:white"><a href="https://doi.org/10.1103/PhysRevLett.101.137201">https://doi.org/10.1103/PhysRevLett.101.137201</a></span><span lang="EN-US">),
in particular this picture (<a href="https://journals.aps.org/prl/article/10.1103/PhysRevLett.101.137201/figures/1/medium">https://journals.aps.org/prl/article/10.1103/PhysRevLett.101.137201/figures/1/medium</a>). 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.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">This is the input I used in case.in0 (the last line triggers the electric field) :<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">TOT XC_PBE (XC_LDA,XC_PBESOL,XC_WC,XC_MBJ,XC_REVTPSS)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">NR2V IFFT (R2V)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> 30 30 360 2.00 1 min IFFT-parameters, enhancement factor, iprint<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">30 1.266176 1.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">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
</span><span lang="EN-US" style="color:black;mso-fareast-language:NL-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 (<a href="https://physics.nist.gov/cgi-bin/cuu/Value?auefld">https://physics.nist.gov/cgi-bin/cuu/Value?auefld</a>),
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?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE">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
<a href="http://dx.doi.org/10.1103/PhysRevB.63.165205">http://dx.doi.org/10.1103/PhysRevB.63.165205</a> ? 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)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE">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.)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE">Thanks for your insight,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE">Stefaan<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE">blebleble s-o calc. M|| 0.00 0.00 1.00<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE">P
</span><span lang="FR-BE" style="color:black;mso-fareast-language:NL-BE">7 99 P<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="FR-BE" style="color:black;mso-fareast-language:NL-BE"> RELA<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="FR-BE" style="color:black;mso-fareast-language:NL-BE"> 5.423516 5.423516 65.082193 90.000000 90.000000 90.000000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="FR-BE" style="color:black;mso-fareast-language:NL-BE">ATOM -1: X=0.00000000 Y=0.00000000 Z=0.12500000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="FR-BE" style="color:black;mso-fareast-language:NL-BE">
</span><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE">MULT= 1 ISPLIT=-2<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE">Fe1 NPT= 781 R0=.000050000 RMT= 2.22000 Z: 26.00000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE">LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE"> 0.0000000 1.0000000 0.0000000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE"> 0.0000000 0.0000000 1.0000000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE">ATOM -2: X=0.00000000 Y=0.00000000 Z=0.37500000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE"> MULT= 1 ISPLIT=-2<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE">Fe2 NPT= 781 R0=.000050000 RMT= 2.22000 Z: 26.00000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE">LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE"> 0.0000000 1.0000000 0.0000000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE"> 0.0000000 0.0000000 1.0000000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE">ATOM -3: X=0.00000000 Y=0.00000000 Z=0.20833333<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE"> MULT= 1 ISPLIT=-2<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE">Fe3 NPT= 781 R0=.000050000 RMT= 2.22000 Z: 26.00000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE">LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE"> 0.0000000 1.0000000 0.0000000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE"> 0.0000000 0.0000000 1.0000000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE">ATOM -4: X=0.00000000 Y=0.00000000 Z=0.29166667<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE"> MULT= 1 ISPLIT=-2<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE">Fe4 NPT= 781 R0=.000050000 RMT= 2.22000 Z: 26.00000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE">LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE"> 0.0000000 1.0000000 0.0000000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE"> 0.0000000 0.0000000 1.0000000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE">ATOM -5: X=0.50000000 Y=0.50000000 Z=0.16666667<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE"> MULT= 1 ISPLIT=-2<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE">Fe5 NPT= 781 R0=.000050000 RMT= 2.22000 Z: 26.00000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE">LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE"> 0.0000000 1.0000000 0.0000000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE"> 0.0000000 0.0000000 1.0000000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE">ATOM -6: X=0.50000000 Y=0.50000000 Z=0.33333333<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE"> MULT= 1 ISPLIT=-2<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE">Fe6 NPT= 781 R0=.000050000 RMT= 2.22000 Z: 26.00000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE">LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE"> 0.0000000 1.0000000 0.0000000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE"> 0.0000000 0.0000000 1.0000000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE">ATOM -7: X=0.50000000 Y=0.50000000 Z=0.25000000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE"> MULT= 1 ISPLIT=-2<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE">Fe7 NPT= 781 R0=.000050000 RMT= 2.22000 Z: 26.00000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE">LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE"> 0.0000000 1.0000000 0.0000000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE"> 0.0000000 0.0000000 1.0000000<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:black;mso-fareast-language:NL-BE"> 8 NUMBER OF SYMMETRY OPERATIONS<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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