[DFTB-Plus-User] About Klines

[giacomo buccella]

Dear Nava,
I suggest to write your questions to the mailing list of dftb+ users or to
post it on the github community.

However, as I can see from the manual, Klines is just a way to set your
preferred k-point path. If you don't like it or it does not suits to your
system, other methods are available. The manual is quite exhaustive on how
is the correct syntax and how these methods are implemented. Please check
to have the most recent version of the code and the relative manual.

Apart from this, I'm not sure I understand what you mean.
The first line is the first k-point, i.e. the starting point for the
K-point sampling. In the next lines you specify how many points you want
and towards which direction.
I don't know why and how these examples have been conceived as they are. As
far as I know, one should choose the k-point grid to be uniform in the BZ,
and dense enough to get accurate results combined with reasonable
computational costs. So I guess that, to construct the grid properly, one
should have an idea of how the atoms dispose themselves in the unit cell.

Hopefully, the community will answer more exhaustively.
Best regards

Giacomo


Il giorno ven 13 gen 2023 alle ore 04:35 Nav Thakur <navthank147 at gmail.com>
ha scritto:

> Respected Giacomo Buccella,
> Recently I have seen your mail in the DFTB+ community and wanted to ask
> some questions. If you have time please help me through this.
> I am new to the computational field. I don't have a basic understanding of
> any of the software packages. I want to start with DFTB+ and I have just
> started from scratch and facing difficulties with certain topics.
>
> These questions might be obvious and fundamental but I want to learn
> without any misunderstanding. I am reading through the recipes listed in
> the manual and on the website. The Kpoints used for the case given left me
> perplexed. Aside from that, KLines'  confused me the most. I've seen videos
> of QM and Siesta as well as WIEN2k, but these band lines were created as a
> result of the Kpoints being established. However, DFTB+ caused
> misunderstanding. I've been following the instructions in the handbook and
> tutorials, so I don't know what I'm missing.
>
> For example, the manual shows,
>
> KPointsAndWeights = KLines{
> 1     0.5   0.0   0.0
> 10    0.0   0.0   0.0
> 10     0.5   0.5   0.5
> 1       0.0    0.0   0.0
> 10     0.5    0.5    0.0
> }
>
> *How are these lines 1, 10, 10, 1, 10 selected in these Klines? *
> I went through the given tutorial and I didn't get how these high
> symmetries points are selected. Please help through this.
>
> In the given tutorial of TiO2,
> https://dftbplus-recipes.readthedocs.io/en/latest/basics/bandstruct.html,
> it has following Klines
>   # ...
>
>   KPointsAndWeights = Klines {
>     1   0.5   0.5  -0.5    # Z
>    20   0.0   0.0   0.0    # G
>    45   0.0   0.0   0.5    # X
>    10   0.25  0.25  0.25   # P
>   }
> }
>
> # ...
>
> *I don't know how these 1, 20, 45, and 10 are selected. How can I just
> signify these lines Z, G, X, and P are in the 1, 21, 66, and 76
> respectively?* Can't I signify others? Moreover, as I went through the
> paper, they have different higher symmetry points than Z, G, X, and P and
> the graphs of the band and DOS structure are also quite different. Can you
> please help in this regard?
>
> I really appreciate any help you can provide.
>
> Thank you for your time.
>
> Sincerely,
>  Nava Thakur
>
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