Dear pablo:
I have a simple question: How can you seeing the effect of the folding
of the 1-d BZ. From the bandstructure or some other properties? Thank you.
wang
> Dear Marcos,
>
> Thank you very much for your answer. I was
> working with (n,n) tubes. I have performed a single cell calculation
> with the 1x1x75 kgrid_monkhorst_Pack and i got the correct results.
> Indeed, I was seeing the effect of the folding of the 1-d BZ.
>
> regards,
>
> pablo
>
>
> ----- Original Message -----
> From: "Marcos Verissimo Alves" <[EMAIL PROTECTED]>
> To: <SIESTA-L@listserv.uam.es>
> Sent: Tuesday, January 16, 2007 2:42 PM
> Subject: Re: [SIESTA-L] DOS SWCNT
>
>
>> Hola Pablo,
>>
>>>
>>> 1- for metallic tubes at least 3 unit cells are needed to obtain a
>>> metallic
>>> DOS
>>
>> Does that mean that with a single unit cell you cannot obtain a
>> metallic DOS? For what kind of nanotubes (zigzag (3*m,0), m integer,
>> or armchair)? This result is weird. Have you relaxed the structure
>> completely, including the nanotube axis? (A good value for the force
>> tolerance would be 0.04 eV/Ang or smaller.) What is the minimum
>> inter-image distance in the x-y plane?
>>
>>>>From this statement I might guess (quite wildly) that you haven't gone
>>> to
>> sufficiently high numbers of k-points for the calculation of the DOS.
>> Do an "experiment": try using
>>
>> %block kgrid_Monkhorst_Pack
>> 1 0 0 0.0
>> 0 1 0 0.0
>> 0 0 75 0.0
>> %endblock kgrid_Monkhorst_Pack
>>
>> in a calculation with a single (totally relaxed) unit cell and check
>> it against the result of the three unit cells, which I suppose you did
>> using the MP grid from item 2. If they match, what you are seeing is
>> the effect of the folding of the 1-d BZ, I would guess.
>>
>>>
>>> 2- %block kgrid_Monkhorst_Pack
>>> 1 0 0 0.0
>>> 0 1 0 0.0
>>> 0 0 25 0.0
>>> %endblock kgrid_Monkhorst_Pack
>>
>> This has to be checked by the total energy convergence with the number
>> of points, although it is not far from the number of points I had to
>> give for good VC relaxation of a graphene unit cell in one of the
>> directions in the sheet plane. Good for structural relaxation, but not
>> DOS calculation (see a previous e-mail by Andrei Postnikov on the
>> subject), which requires a substantially higher amount of k-points.
>>
>> Also, from the block above I suppose that your nanotube axis is
>> aligned with the z-axis. Correct?
>>
>>>
>>> 3- PAO.BasisSize DZP
>>
>> Ok, good basis, but be carfeul with the Energy shift.
>>
>>>
>>> 4- MeshCutoff 400. Ry
>>
>> Might be a bit too much, unless you are going to a very strict energy
>> convergence. My experience is that 300 Ry does the job fine - even 250
>> wouldn't be too bad.
>>
>>>
>>> 5- PBE perfoms better than LDA but, the results with the later are
>>> reasonable.
>>
>> Makes sense. Again, depends on what you want. Check against the
>> infinite number of calculations in the literature both with siesta and
>> PW basis sets.
>>
>>>
>>> 6- the r for the TM pseudo was 1.5
>>
>> If it gives you good agreement of pseudo-eigenvalues and logarithmic
>> derivatives against the all-electron results, then don't worry, be
>> happy... :)
>>
>> Marcos
>>
>>
>> --
>> Dr. Marcos Verissimo Alves
>> Post-Doctoral Fellow
>> Condensed Matter and Statistical Physics Sector
>> International Centre for Theoretical Physics
>> Trieste, Italy
>>
>> --------
>>
>> I have become so addicted to vi that I try to exit OpenOffice by
>> typing :wq!
>>
>>
>> --
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