[Wien] zigzag potential (remaining questions)
Peter Blaha
pblaha at theochem.tuwien.ac.at
Fri Jan 5 16:54:36 CET 2018
Hallo Stefan,
Thanks for the suggestions, I'll take them.
Please test the plotted potential again, but WITHOUT selfconsistency !!!
i.e.
Start from a converged calculation WITHOUT field.
Put the field into case.in0 and R2V
x lapw0
cp the potential to case.clmvalup
x lapw5 -up (-c not needed)
I'd expect there is a counteracting field developing during scf, which
reduces the applied field.
On 01/05/2018 03:53 PM, Stefaan Cottenier wrote:
> Hello Peter,
>
>> 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.
>
> I did that, for the case.struct pasted at the end, in the following way:
>
> runsp -so
> cp case.vtotal case.clmvalup
> x lapw5 -c -up
>
> where this was the content of case.in0 (R2V and electric field):
>
> TOT XC_PBE (XC_LDA,XC_PBESOL,XC_WC,XC_MBJ,XC_REVTPSS)
> R2V IFFT (R2V)
> 30 30 360 2.00 1 min IFFT-parameters, enhancement factor, iprint
> 30 1.266176 1.
>
> and where this was the content of case.in5c (a single line through the vacuum and through the slab, in a region as far as possible from the nuclei):
>
> 0.50 0.00 0.00 1
> 0.50 0.00 1.00 1
> 0.50 0.00 0.00 1
> 3 3 3
> 100 1
> RHO
> ATU VAL NODEBUG
>
> The result is a graph where I do see the kink halfway the unit cell. That confirms that the default zigzag potential is as shown in Fig. 6 of http://dx.doi.org/10.1103/PhysRevB.63.165205 . [while writing this, Gavin's analysis appeared on the list, which confirms this]
>
> The value of the field is not fully clear, however. In the vacuum region of the unit cell, there is a section of length 16.4349 bohr where the potential is nicely linear. The potential change over that interval is 0.270806 Ry. The absolute value of the constant electric field in that vacuum region is therefore 0.270806/16.4349 = 0.016477 Ry/bohr. That's 0.423 V/Ang.
>
> However, for the EFIELD value of 1.266176 (see case.in0 above) and c lattice parameter of 65.082193 bohr, the specified electric field should be according to the usersguide 1.266176/65.082193 = 0.019455 Ry/bohr = 0.500 V/Ang.
>
> That means there is no issue with a possible factor 2 (the statement in the usersguide is correct), but now I'm puzzled about the difference between 0.423 and 0.500 V/Ang. That looks to be too large to be noise...?
>
>> PS: I'll take up any "explicit" suggestion for the UG. (but not just "please
>> improve it").
>
> Point taken, yet I was in need of the hints hereabove before I could make sense of it. These are the changes I would now propose:
>
> * I suggest to remove the line 317 in eramps.f that Gavin mentions, in order to print the applied potential in case.output0 by default. It will not hinder anybody as this option is rarely used, and for those using it it will at least tell unambiguously which applied potential is present.
>
> * This is a more explicit text for the usersguide, that would have prevented most of my doubts:
>
> =======
> IFIELD: number of Fourier coefficients to model the zig-zag potential, also known as the 'analytic triangular ramp' (mode=0, default). Typically use IFIELD=30 (the maximal value is IEFIELD=999, but you should stay way below that). This zig-zag potential reaches maxima at z=0 and z=1, and a minimum at z=0.5 (see fig. 6 of [Stahn et al., 2001]). Using IFIELD=-999 (with a random value for EFIELD) lists in case.output0 the other available modes (forms) of electric fields. You can select mode n by specifying IFIELD=n*1000 (e.g. IFIELD=4000 gives you mode 4). The mode that is being used, is printed at the top of case.output0.
>
> EFIELD: value (amplitude) of the electric field. The electric field (in Ry/bohr) corresponds to EFIELD/c, where c is your c lattice parameter. In order to have the electric field in Volt/Angstrom, multiply EFIELD/c by 13.6/0.529177.
>
> WFIELD: optional value for lambda (see output of IFIELD=-999).
> ==========
>
> Best regards,
> 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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--
P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
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