# [Pw_forum] Slow calculation of (5, 5) CNT transmission and complex bands.

Gabriele Sclauzero gabriele.sclauzero at epfl.ch
Tue Aug 9 18:40:28 CEST 2011

```Dear Chengyu Yang,

(1) the number of k-points you need to use in order to get a nice band structure plot depends obviously on the details of the geometry (in particular, on the size of the BZ, which is related to the size of the unit cell, and on the number and "flatness" of the bands, to resolve correctly the band crossings) and also on the lenght of your path, obviously.
Your band structure doesn't tell much to me, since I've never computed CNTs so far, but you could easily check your results with the available literature.
(2) Which example are you speaking of? Your questions look obscure to me. Please try to be more clear and explain exactly what you are refering to (bulk Al or Al wire? conductance, complex band structure, or standard electronic structure calculation? Where are those 50 k-points? I can't find them...)

HTH

Gabriele SclaUzero

PS:
there is no need to send also a duplicate message to my email address since I'm (obviously) subscribed to this mailing list and I can get your posts through the list

Il giorno 09/ago/2011, alle ore 17.37, chengyu yang ha scritto:

> Dr. Sclaizero and all,
>      Thanks for your reply. It really gave me a clue.However, about the k points, I still have some problem.
>      (1) I heard that to calculate bandstructure, one need to use more than 20 k points to get a reliable result, that's why I was looking for more k points. I did only use the three high symmetry k points in the nscf calculation, but the final result seems to be too simple to be true. I attached them for you to have a look.
>      (2) In the conductance example for Al, I see they used 50 k points to get a bandstructure, and I was wondering how did they get them? I can only find at most 10 high symmetry points for Al. Do we need the same amount/scale of K point ? If so, how?
>
> k points in the al.nscf.in:
>
> K_POINTS
>      50
> 0.00   0.00       0.00000000      0.00000000
> 0.00   0.00       0.00721538      0.00721538
> 0.00   0.00       0.01443075      0.01443075
> 0.00   0.00       0.02164613      0.02164613
> 0.00   0.00       0.02886150      0.02886150
> 0.00   0.00       0.03607688      0.03607688
> 0.00   0.00       0.04329225      0.04329225
> 0.00   0.00       0.05050763      0.05050763
> 0.00   0.00       0.05772300      0.05772300
> 0.00   0.00       0.06493838      0.06493838
> 0.00   0.00       0.07215375      0.07215375
> 0.00   0.00       0.07936913      0.07936913
> 0.00   0.00       0.08658450      0.08658450
> 0.00   0.00       0.09379988      0.09379988
> 0.00   0.00       0.10101525      0.10101525
> 0.00   0.00       0.10823063      0.10823063
> 0.00   0.00       0.11544601      0.11544601
> 0.00   0.00       0.12266138      0.12266138
> 0.00   0.00       0.12987676      0.12987676
> 0.00   0.00       0.13709213      0.13709213
> 0.00   0.00       0.14430751      0.14430751
> 0.00   0.00       0.15152288      0.15152288
> 0.00   0.00       0.15873826      0.15873826
> 0.00   0.00       0.16595363      0.16595363
> 0.00   0.00       0.17316901      0.17316901
> 0.00   0.00       0.18038438      0.18038438
> 0.00   0.00       0.18759976      0.18759976
> 0.00   0.00       0.19481513      0.19481513
> 0.00   0.00       0.20203051      0.20203051
> 0.00   0.00       0.20924588      0.20924588
> 0.00   0.00       0.21646126      0.21646126
> 0.00   0.00       0.22367663      0.22367663
> 0.00   0.00       0.23089201      0.23089201
> 0.00   0.00       0.23810739      0.23810739
> 0.00   0.00       0.24532276      0.24532276
> 0.00   0.00       0.25253814      0.25253814
> 0.00   0.00       0.25975351      0.25975351
> 0.00   0.00       0.26696889      0.26696889
> 0.00   0.00       0.27418426      0.27418426
> 0.00   0.00       0.28139964      0.28139964
> 0.00   0.00       0.28861501      0.28861501
> 0.00   0.00       0.29583039      0.29583039
> 0.00   0.00       0.30304576      0.30304576
> 0.00   0.00       0.31026114      0.31026114
> 0.00   0.00       0.31747651      0.31747651
> 0.00   0.00       0.32469189      0.32469189
> 0.00   0.00       0.33190726      0.33190726
> 0.00   0.00       0.33912264      0.33912264
> 0.00   0.00       0.34633802      0.34633802
> 0.00   0.00       0.35355339      0.35355339
>
>
>   Thanks for your patience.
>
> Best regards.
>
> Chengyu Yang
> MMAE,University of Central Florida
>
>
>
>
> <55bands1.ps><55bands3.ps>_______________________________________________
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§ Gabriele Sclauzero, EPFL SB ITP CSEA
PH H2 462, Station 3, CH-1015 Lausanne

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