[Pw_forum] Yet another question about graphene bandstructure

[jbobak]

Hi Hadi,

Thank you so much for all the help!

Two quick questions, when you say the K-mesh is not dense enough do you
mean in the original SCF calculation (18x18x1) or do you mean I should
choose more points along the Gamma->K->M->Gamma path?

I have tried a variety of values for ecut (37, 47, 57, 67), but I have not
been specifying ecutrho -- why is the default value not appropriate in
this case? I thought 4 x ecut was ok for pseudopotentials that are not
ultrasoft.

Thank you again,
Julia

> Dear Julia,
>
> They are of course in the reciprocal space no matter you want them to be
> or not! If your K-mesh is dense enough (which is not in your current
> input) and along the right paths (Which still aren't:
> GAMMA-to-M-to-K-to-GAMMA), then there are some parameters you need to
> check such as smearing/K-points/ecut/ecutrho convergence.
>
> Your smearing looks high to me and your ecut is too much for a PAW pseudo
> potential that you are using. Also you need to specify ecutrho as well
> because the default value is used in the case of norm conserving one.
>
> HTH.
>
> Hadi.
>
> -----Original Message-----
> From: pw_forum-bounces at pwscf.org [mailto:pw_forum-bounces at pwscf.org] On
> Behalf Of jbobak
> Sent: 10 March 2014 18:14
> To: PWSCF Forum
> Subject: Re: [Pw_forum] Yet another question about graphene bandstructure
>
> Hi Hadi,
>
> Thank you for your quick response! I have tried that K-path also (I remain
> confused as to whether K-paths are in real or reciprocal space, so I tried
> both) with a similar result.
>
> Julia
>
>> Dear Julia,
>>
>> I guess your K-path is not entirely coincides with the high symmetry
>> points for graphene. Make sure you span the following routes with
>> enough
>> K:
>>
>> 0	0	0
>> 0.666	0.333	0
>> 0.5	0.5	0
>> 0	0	0
>>
>>
>> HTH,
>>
>> Hadi.
>> -----Original Message-----
>> From: pw_forum-bounces at pwscf.org [mailto:pw_forum-bounces at pwscf.org]
>> On Behalf Of jbobak
>> Sent: 10 March 2014 17:04
>> To: pw_forum at pwscf.org
>> Subject: [Pw_forum] Yet another question about graphene bandstructure
>>
>> Hi all,
>> I've searched the forum for this question, but nobody seems to be
>> having quite the same issue, so I expect I'm doing something uniquely
>> stupid. I am trying to calculate the band structure of graphene (using
>> Espresso
>> 5.0.3) for practice before I use a more complicated system. I do an
>> SCF calculation with just the unit cell (2 atoms) with automatic
>> k-points 18
>> 18 1 0 0 0. Then I do a band structure calculation with k-points as
>> follows:
>>
>> K_POINTS {tbipa}
>> 7
>> 0.00000 0.00000 0.00000 1
>> 0.28868 0.16666 0.00000 1
>> 0.57735 0.33333 0.00000 1
>> 0.43301 0.41666 0.00000 1
>> 0.28868 0.50000 0.00000 1
>> 0.14435 0.25000 0.00000 1
>> 0.00000 0.00000 0.00000 1
>>
>> I then run bands.x, followed by plotband.x which I run interactively.
>> Everything works fine in that I get no errors, but the bandstructure
>> plot is wrong (see attached pdf). The bands should cross at the K
>> point. I think the problem has something to do with the k-points,
>> which is why I have reproduced them above, but I have also attached
>> the relevant input and output files. Could it be because the
>> high-symmetry k-points I selected are not present in the automatically
>> selected grid?
>>
>> Thank you so much for any help,
>> Julia Bobak
>>
>> Research Assistant
>> University of Victoria, Victoria, BC, CANADA
>>
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>
>
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