[Wannier] DOS calculation with full and IBZ giving different results
Raul Laasner
raullaasner at gmail.com
Sat Dec 13 13:36:07 CET 2014
Hi
Your suspicion was well-founded. The ab-initio eigenvalues are correct, but
the Wannier functions are actually not entirely converged. In fact, the
difference in results seems to be greater in regions of poorer convergence.
I somehow assumed the Wannier interpolated quantities always have the
correct symmetries, even if WFs themselves are not fully converged. I
should carefully reread the original papers ... Thanks for the help.
Raul
On Sat, Dec 13, 2014 at 10:40 AM, Giovanni Pizzi <giovanni.pizzi at epfl.ch>
wrote:
>
> Hi Raul,
> thank you for your detailed answer.
> It seems to me that even the energies may not be the same in the points
> that you expect to be equivalent. A couple of further questions then, sorry
> if they may seem trivial…
>
> 1. Did you check that the structure has exactly the exact symmetry that
> you expect?
> 1bis. Can you check with the ab-initio code to check the eigenenergies at
> the points that should be degenerate to see if the energies are the same?
> 2. Did you check that the Wannier functions are well converged?
> 2bis. Can you check that the interpolated bandstructure with Wannier
> functions satisfy the symmetry that you expect, e.g. doing a band plot
> along two equivalent bands?
>
> Thanks,
> Giovanni
>
>
> --
> Giovanni Pizzi
> Post-doctoral Research Scientist
> EPFL STI IMX THEOS
> MXC 340 (Bâtiment MXC)
> Station 12
> CH-1015 Lausanne (Switzerland)
> Phone: +41 21 69 31124
>
>
>
>
> On 13 Dec 2014, at 00:25, Raul Laasner wrote:
>
> Thanks for responding. Yes, also without adaptive smearing the results
> differ a little bit. However, the difference decreases with k-mesh size.
> With dos_kmesh 10 the difference is very small and with lower values the
> results are identical.
>
> For debugging purposes, I tried dos_kmesh 2 with adaptive smearing. If I
> put
>
> 8
> 0.00000000E+00 0.00000000E+00 0.00000000E+00 0.12500
> 5.00000000E-01 0.00000000E+00 0.00000000E+00 0.12500
> 0.00000000E+00 5.00000000E-01 0.00000000E+00 0.12500
> 5.00000000E-01 5.00000000E-01 0.00000000E+00 0.12500
> 0.00000000E+00 0.00000000E+00 5.00000000E-01 0.12500
> 5.00000000E-01 0.00000000E+00 5.00000000E-01 0.12500
> 0.00000000E+00 5.00000000E-01 5.00000000E-01 0.12500
> 5.00000000E-01 5.00000000E-01 5.00000000E-01 0.12500
>
> into my kpoint.dat, then I get the correct result. However, with
>
> 3
> 0.00000000E+00 0.00000000E+00 0.00000000E+00 0.12500
> 5.00000000E-01 0.00000000E+00 0.00000000E+00 0.50000
> 5.00000000E-01 5.00000000E-01 0.00000000E+00 0.37500
>
> the results again differ. (I forgot to say that NaI has the rock-salt
> structure.)
>
> I had a look at the loop that performs the main calculation in dos_main
> and inserted
>
> write(*,'(*(f7.5,1x))') kpt, dos_k(452,1)*kweight
>
> after the 'dos_all=dos_all+dos_k*kweight' line to see how each k-point
> contributes to the sum. Here the index 452 refers to some energy level that
> I randomly picked. The result is
>
> 0.00000 0.00000 0.00000 0.22149
> 0.00000 0.00000 0.50000 4.22194
> 0.00000 0.50000 0.00000 3.32614
> 0.00000 0.50000 0.50000 0.00000
> 0.50000 0.00000 0.00000 1.11124
> 0.50000 0.00000 0.50000 0.00000
> 0.50000 0.50000 0.00000 0.00000
> 0.50000 0.50000 0.50000 0.45465
>
> where the last column is the corresponding density. By symmetry, I would
> expect only 3 numbers to differ in this column, but this is not the case.
> Have I misunderstood something?
>
> As another check, before the main loop, I put
>
> kpt = [0.5,0.0,0.0]
> call get_eig_deleig(kpt, eig, del_eig, HH, delHH, UU)
> print*, norm2(del_eig(1,:))
> kpt = [0.0,0.5,0.0]
> call get_eig_deleig(kpt, eig, del_eig, HH, delHH, UU)
> print*, norm2(del_eig(1,:))
>
> which prints the magnitude of the band derivative of the first band at
> these two k-points, with the result
>
> 0.44616527636129560
> 3.1348138571982227E-003
>
> Shouldn't these numbers be the same by symmetry?
>
> Finally, I'm not sure what you mean by 'units for the kpoints' as I'm
> only entering the reduced coordinates.
>
> Raul
>
> On Fri, Dec 12, 2014 at 5:38 PM, Giovanni Pizzi <giovanni.pizzi at epfl.ch>
> wrote:
>>
>> Dear Raul,
>> in order to understand if the problem is in the dos routine, or in the
>> routine that generated the IBZ points, could you run the same thing (i.e.
>> DOS, with and without wanint_kpoint_file), but using dos_adpt_smr=False,
>> and instead a fixed-width smearing? (e.g. a gaussian smearing)
>> And then compare the results, and report them here?
>>
>> As a further detail, could you also check if the units for the kpoints
>> that you are passing in the wanint file are the one expected by the code?
>>
>> Thanks,
>> Giovanni
>>
>>
>>
>> On 12/12/2014 11:09 AM, Raul Laasner wrote:
>>
>> Dear all,
>>
>> When I calculate the density of the lowest conduction states of NaI
>> (see attachment), I get different results for using k-points from the full
>> and irreducible Brillouin zones. The difference is smaller when the k-mesh
>> is allowed to use less symmetries, e.g. only the time reversal symmetry.
>> There is no difference if the 'kpoint.dat' file contains the full BZ. This
>> suggests the code I use for generating IBZ points might be in error, but I
>> get the same results with both abinit and elk (they deliver different, but
>> equivalent IBZ points). Could it be that the DOS calculation is very
>> sensitive to small numerical inaccuracies and this leads to slightly
>> different results for full and irreducible BZs? The DOS related part of my
>> input file is the following:
>>
>> dos true
>> dos_kmesh 20
>> dos_adpt_smr true
>> wanint_kpoint_file false # true for the second run
>>
>> The difference is also present with dos_kmesh 50. Please ask for other
>> details I'm not showing. Any suggestions are welcome.
>>
>> Thanks,
>> Raul Laasner
>>
>>
>> --
>> Raul Laasner
>> Institute of Physics
>> University of Tartu
>> Ravila 14c, 50411, Estonia
>> e-mail: raullaasner at gmail.com
>> cell: (+372)5182268
>>
>>
>> _______________________________________________
>> Wannier mailing listWannier at quantum-espresso.orghttp://mailman.qe-forge.org/cgi-bin/mailman/listinfo/wannier
>>
>>
>>
>> --
>> Giovanni Pizzi
>> Post-doctoral Research Scientist
>> EPFL STI IMX THEOS
>> MXC 340 (Bâtiment MXC)
>> Station 12
>> CH-1015 Lausanne (Switzerland)
>> Phone: +41 21 69 31124
>>
>>
>> _______________________________________________
>> Wannier mailing list
>> Wannier at quantum-espresso.org
>> http://mailman.qe-forge.org/cgi-bin/mailman/listinfo/wannier
>>
>>
>
> --
> Raul Laasner
> Institute of Physics
> University of Tartu
> Ravila 14c, 50411, Estonia
> e-mail: raullaasner at gmail.com
> cell: (+372)5182268
>
>
>
--
Raul Laasner
Institute of Physics
University of Tartu
Ravila 14c, 50411, Estonia
e-mail: raullaasner at gmail.com
cell: (+372)5182268
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