Messages

31

General Questions and Answers / NEGF not Convergence：the electron distribution is wrong how to plot deltaH

« on: December 5, 2018, 05:25 »

Hi all:
I face an issue about device convergence, and according to the NEGF Convergence Guide, I first need to check the central region is long enough or not. But my understanding is because the electron distribution is wrong for not convergence,   
so the resulting plot deta_Ha is also wrong,
and then how could I know the convergence issue is due to the length of the central region.

thanks very much if someone can help me.

cheers

32

General Questions and Answers / about the initial spin of system containing Hydrogen atoms

« on: November 27, 2018, 07:33 »

Hi all:

a few days ago, I found a page titled "potential problem xxx", about initial spin setting up. I remember it said it is better to set initial spin 0.99 not 1 to avoid the convergence  problem,
but I cannot remember where to find the page online.
is there anyone kindly to let me know where it is now

3x very much!

33

General Questions and Answers / the fixed-spin can only for the spin direction not spin magnitude?

« on: October 24, 2018, 14:33 »

Hi all：
i want to fix the magnitude of spin for some atoms in molecular, is there possible now?


thanks very much?

34

General Questions and Answers / the bader charge analysis can be used to device configuration?

« on: October 24, 2018, 14:27 »

hello all:
I receive a reviewer comments, he required me that the Milliken analysis would be accurate to my device configuration , and ask me to do bader analysis,

so i am wondering how to calculation bader charge because i look up it is only for bulk configuration , not the device configuration.
now my version 2018.06

thanks very much

35

General Questions and Answers / Re: is it possible to reproduce a very very tiny bandgap~2mev

« on: May 8, 2018, 14:01 »

Although it's possible there could be some details of the calculation that are not share properly in the paper, and you need very high accuracy or some special tricks, I find some parts of this paper unclear. Look at the dispersion close to M: why is  the branching at -1 eV happening not exactly at M but after? Normally the bands branch at the symmetry points... This could indicate an index error in the plotting, which also would affect the interpretation of the bands at K. I would also like to see the points at K, not just the lines.  I am not saying the paper is wrong, but they are making it hard to understand their data, and for such small values as 2 meV one should be very careful. I would like to see e.g. the effect of the k-point sampling which is know to affect the band structure of graphene very much, unless you sample the K point properly, which I'm not sure is done with a 5x5 sampling on a 4x4 or 5x5 supercell.

Dear Sir:

thank you for your kindly relpy.

in last few days, i was searching other literature  about the tiny gap issue about Graphene/Mos2. and found a paper  APPLIED PHYSICS LETTERS 105, 031603 (2014), in which they used SIESTA and dzp basis  to model the  heterostructures, and found zero bandgap,so i though the results we used ATK-DFT would be similar to that paper.
on the other hand, i am woundering it is necessary to concern such tiny gap? as  Petr Khomyakov said, 2 meV is of relevance for ultra-low temperatures < 30 K only

thanks again .

36

General Questions and Answers / Re: how to specify the K point not along the high symmetrical direction

« on: May 8, 2018, 13:42 »

thank you sir.

i will try it

37

General Questions and Answers / Re: how to specify the K point not along the high symmetrical direction

« on: May 3, 2018, 15:42 »

I was able to detect the issue with Sublime Text. It allows you to specify how spaces and tabs should be treated. I think most decent programming editors has such options, so if you prefer another editor, then you should be able to find some guides online.

thank you very much, i will try it .

just now, i checked ultraedit editor which i am using , it is pity it seems has no python support.

38

General Questions and Answers / Re: is it possible to reproduce a very very tiny bandgap~2mev

« on: May 3, 2018, 15:36 »

You may use  LCAO basis set combined with SG15 pseudopotential (or pseudoDojo that will be available in O-2018.06), you will  then have an option to choose between Medium, High and Ultra accuracy for the LCAO basis set functions.

The exact answer to your question depends on the specific system of study, and requires actual calculation for verification of the LCAO basis set accuracy. However, I would like to notice that the DFT-PAW approach is also an approximation to all-electron DFT calculations,  meaning that 2 meV band gap obtained in VASP can be very much within the accuracy of the method. In that sense, one would have to do accurate all-electron calculations for having a reference.

From the physical point of view, band gap of 2 meV is of relevance for ultra-low temperatures < 30 K only. You have to be aware that DFT may significantly underestimate band gaps of semiconductors, or even predict no gap, e.g., for bulk Ge.

Note that FHI pseudopotential and LCAO basis sets associated with it are less accurate than SG15 pseudoptential/LCAO basis sets.

thank you for your detailed help .

indeed, with DFT, using  LCAO, i get the zero gap. so i have no ideas what to do.

as you mentioned, SG15 is only available in the coming version 2018??

because i have not seen this functional in 2017.12.

the results i want to reproduce is Nanoscale, 2011, 3, 3883,and want to get the bandstructure as figures enclosed.

39

General Questions and Answers / Re: how to specify the K point not along the high symmetrical direction

« on: May 3, 2018, 14:54 »

My guess is that the original script contains a mix between tabs and spaces, which is something python has problems with. Some editors can show the difference between tabs and spaces, which might be helpful.

thanks for your kindly suggesting, and would you let me know which editor can detect the different between blank and tabs?

thanks very  much.

40

General Questions and Answers / is it possible to reproduce a very very tiny bandgap~2mev

« on: May 3, 2018, 03:52 »

Hi Sir:
i want to reproduce the bandgap ~2meV, which is calculated by PAW pp with VASP,
so i am wondering is it possible to reproduce it,  because at present, i used DZP, and try as many as possible K points,  in on direction i used 101 K along high symmetry line, it seems not work, i think maybe LCAO have not such precision ?
please give me a hint.

thanks very much .

 
 

41

General Questions and Answers / the iteration control, the mixing variable and and algorith can not be changed

« on: May 3, 2018, 03:43 »

Dear Sir;
 in my VNL gui, (2017.12 VERSION ,)the new calculator--->iteration control>>>> mixing variable and and algorith can not show the drop down option.please see the figure. others option seems OK

please check it

thanks very much.

my system is linux, Linux version 2.6.32-220.el6.x86_64 (mockbuild@x86-004.build.bos.redhat.com) (gcc version 4.4.5 20110214 (Red Hat 4.4.5-6) (GCC)

42

General Questions and Answers / Re: how to specify the K point not along the high symmetrical direction

« on: May 3, 2018, 03:17 »

thanks very much, it works now.

although i have not make clear what is wrong with my original script.

 

43

General Questions and Answers / Re: how to specify the K point not along the high symmetrical direction

« on: May 1, 2018, 04:38 »

Thank your for your reply.

enclose is my own  script adding the def function .

please help me, i am very sorry i am not familiar with python

44

General Questions and Answers / Re: how to specify the K point not along the high symmetrical direction

« on: April 30, 2018, 14:48 »

Thank you for your reply,
however, i copy the sentence to myown script
the errors occurs. so please do me a favor what is wrong with the syntax.




+------------------------------------------------------------------------------+
  File "./band .py", line 377
                "G"  : numpy.array((0.0, 0.0, 0.0)),
    ^
SyntaxError: invalid syntax


the paragraph is following:
def mysym():
        return {
            "G"  : numpy.array((0.0, 0.0, 0.0)),
            "K"  : numpy.array((2./3., 1./3., 0.0)),
            "Y"  : numpy.array((0.0, 0.5, 0.0)),
            "X"  : numpy.array((0.5, 0.0, 0.0)),
            "V"  : numpy.array((0.5, 0.5, 0.0)),
        }

bulk_configuration.bravaisLattice().symmetryPoints = mysym





bandstructure = Bandstructure(
    configuration=bulk_configuration,
    route=['G','X','K','G' 'V','Y','G'],
    points_per_segment=51,
    bands_above_fermi_level=30
    )
nlsave('band.hdf5', bandstructure)


thanks again

45

General Questions and Answers / how to specify the K point not along the high symmetrical direction

« on: April 30, 2018, 07:04 »

Hi
I am doing a band structure calculation, and I want to know one K point that  is not along the high symmetrical direction.
so I am wondering how to specify the Fraction position in BZ, because in the option where can not input K,M,G,V ..
I need your help

thank you very much