Messages

1

Scripts, Tutorials and Applications / Re: Script for calculate the bandgap.

« on: May 26, 2009, 00:43 »

The way the picture looks, this system is metallic and hence there is no band gap. The script assumes a band gap exists; if it doesn't you may indeed get weird results. This is a good example of the importance of not just applying a script like this and trust the results blindly, but one must always investigate the results in detail.

Do u consider any  single line around Fermi level as 0 bandgap?Should it be between "somehing"

2

Scripts, Tutorials and Applications / Re: Script for calculate the bandgap.

« on: May 25, 2009, 03:23 »

I have got some picture,where is single E(k) line around the Fermi level
And seemed that bandgap script consider that line as valence band
  band gap is calculated around 1Ev not 4Ev
Is that line could be error and real bandgap is 4EV?
http://www.hot.ee/suurfail//BN5-5-1.JPG

3

General Questions and Answers / Re: Choice of basis

« on: May 23, 2009, 18:03 »

Thx ,that explanantion was good.
But i have difficulties understand terms

DoubleZeta; two basis orbitals for each valence orbital

What is term "(two)basis" orbital?

DoubleZeta plus one basis orbital for the first unoccupied shell

What is term unoccupied "shell"?
Is it same as unoccupied (unit)cell?

4

General Questions and Answers / Re: Choice of basis

« on: May 22, 2009, 02:30 »

ok i understand the basic.
Lets take simple carbon graphene layer.They should have 3 neighbour atoms.
Does it mean,that SZ deals with FIRST  neighbour atoms valence orbitaks(minimum conditions)
DZ deals with FIRST and SECOND neighbour atoms valence orbitals?


http://www.hot.ee/suurfail//neibourh%20atoms.PNG
Here is picture which reflects my thoughts

5

General Questions and Answers / Re: Choice of basis

« on: May 21, 2009, 13:45 »

  Hi!
 Can u briefly say what is SZ,DZ,SZP,DZP,DZDP?
And how these methods are correlated with Tight binding model?
How many neighbours atoms we take into account of calculating bands?

6

Future Releases / Re: NanoLanguage editor

« on: May 20, 2009, 19:12 »

Yes we need several script editor.And marked lines would be very helpful.
But after all ""Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius -- and a lot of courage -- to move in the opposite direction."
No doubt,simple notepad is the best!

7

Scripts, Tutorials and Applications / Re: Script for calculate the bandgap.

« on: May 12, 2009, 19:23 »

Actually i tried to calculate C nanotubes band gaps
For A-type(n,n) nanotubes there wasnt much problems.Bandgaps were close to the zero
But when i calculated Z-type(n,0) nanotubes i met serious problems
For example (6,0) nanotube DG and IG were accordingly 7.02eV,-0.46eV
And (7,0) nanotubes DG and IG were both around 0,45eV

In theory (6,0) should be semimetallic close to zero and (7,0) must be semiconductor
I tried also nanoribbons and there was same problems

I used N=10..100 but actually it doesnt change result must,mayby 20%
So i think problem is not there

Mayby i have messed  up creating nc file?(k=1,1,50) ,other default parametres
By the way when Indirect Gap is negative,what it means?

8

Scripts, Tutorials and Applications / Re: Script for calculate the bandgap.

« on: April 17, 2009, 22:56 »

Hi,i tried to use standard 4,4 nanotube with this script and it resulted 0.06eV Direct and Indirect bandgap.
In theory it shoud be zero.Whats wrong?

What is "Direct" and "Indirect" band gaps?

9

General Questions and Answers / Re: Band structure

« on: April 16, 2009, 04:20 »

thx for bothering any answer.i am aware, that DOS is good for band gap .But there arise another problem  with plotting DOS(i cant do it)
Also band structure graphs on the books are "too" beatiful,its easy to determine band gap.
Is it possible to measure band gap somehow?
By the way ,are nanotube grower energy bands  calculated before?And it plots precalculated picture?
The tutorial is great idea and i waiting for it!

10

General Questions and Answers / Band structure

« on: April 15, 2009, 07:28 »

Im intrested in finding band structure for graphenes and nanotubes.
My goal is to get these parametres
1)Fermi level
2)Band gap
3)Brillione zone direction
4)Is it metallic or semiconducting?

Should i choose "method" Brillouin Zone Integration?And can u explain what are these number of k points (A)(B) (C)?
In analysis tab when im intrested calculating energy bands,but i really dont understand what are below tab Band line points(scaled k-points)

About plotting graph.Along the x-axis i see only gamma to K or smth.But how does i know is "gamma" correspond to k=+-pii/a for example.When i resize plot,then there are nothing left in x-axis
I have no idea how to get band gap(Fermi level can be  calculated another analyses tab i presume)
Same problem for determining "metallic or semiconducting" state,because plot seems so crazy and im not sure making right consequences about their state

I looked at ATK tutorial(part 2,page 12) and saw some advanced graph.Is it possible to get the script?

11

Scripts, Tutorials and Applications / Re: Graphene nanoribbon tutorial

« on: March 31, 2009, 23:52 »

armchair = False   # False -> zigzag
width = 14          # ribbon width across, number of layers (must be even for zigzag)
repetitions = 1    # repetitions of the minimal unit along the ribbon
PAC = True         # False -> molecule

# The two atoms in the "graphene" basis
atom1 = Boron
atom2 = Nitrogen

# Set to false to remove the edge hydrogen termination
include_H = True

Thx ,that script seems perfect.
Altough, is  that script only for armchair(x,x) and zigzag(x,0) structures
what about chiral ?

12

Scripts, Tutorials and Applications / Re: Graphene nanoribbon tutorial

« on: March 31, 2009, 17:15 »

Thx for replies.

You basically have to do this by hand for the ribbons, either you want to change the existing structure or build some new structure from scratch. What exactly do you want to change?

I want to do some simple operation
graphene sheet with width=6 and rep=2
I want to replace some C atoms to B and N atoms.I dont want to change structure just simple atom replacement.Or another words i would like to see graphene sheet which is made in Boron or Nitrogen

If i go to the atomic manipulator i cant change nothing
Second chance i went to the Molecular Builder and did some replacements and back to the Manipulator and all seemed ok.But when i dragged it to the Nanolanguage scripter i didnt see quantities availability "ENERGY BANDS" for calculating.Instead of "Energy bands" i see "Energy Spectrum Molecular Energy spectrum"

Is there some theoretical  reason for that?


Second question about Energy density.In some cases it shows beatiful DOS diagramm,other cases it shows only preview for nanoscope?

13

Scripts, Tutorials and Applications / Re: Graphene nanoribbon tutorial

« on: March 23, 2009, 18:16 »

I have several question due to graphene nanoribbon
1)Why there are hydrogen atoms,can we just delete it?
2)when we calculate energy bands for graphene nanoribbon then the paralel axes shows nothing
Should be gamma to K or how we know it?
3)How we can delete/replace atoms in "electrode" part?
4)Can u describe briefly what is transmission spectrum?I didnt find much from books.
There is no efficient data for x and y-axis .Y-axis says word "Transmission",x-axis says "E-Ef(Ev)"
Is there shown Fermi level?

14

General Questions and Answers / Re: About the Number of k-points ?

« on: March 17, 2009, 20:31 »

My problem is same-selecting the bottom tab parameteres
For example graphene tutorial
Adition to the power spectrum there are other possible quantities.Electron density,Eigenvalues,Eigenstates etc

Could u do some example? for example simple graphene?

15

General Questions and Answers / Re: Z-shaped nanoribbon junction

« on: March 17, 2009, 06:35 »

right_electrode_coordinates = (numpy.array (  [[  8.45349407,   7.5       ,   1.42086005],
                         [  8.45349407,   7.5       ,   2.8417201 ],
                         [  9.68399525,   7.5       ,   3.55215001],
                         [  9.68399525,   7.5       ,   0.71043003],
                         [ 10.91449547,   7.5       ,   1.42086005],
                         [ 10.91449547,   7.5       ,   2.8417201 ],
                         [ 12.14499664,   7.5       ,   3.55215001],
                         [ 12.14499664,   7.5       ,   0.71043003],
                         [ 13.37549782,   7.5       ,   1.42086005],
                         [ 13.37549782,   7.5       ,   2.8417201 ],
                         [ 14.60599804,   7.5       ,   3.55215001],
                         [ 14.60599804,   7.5       ,   0.71043003],
                         [ 15.83649921,   7.5       ,   1.42086005],
                         [ 15.83649921,   7.5       ,   2.8417201 ],
                         [  7.5       ,   7.5       ,   0.87036002],
                         [  7.5       ,   7.5       ,   3.39222002],
                         [ 16.78999329,   7.5       ,   0.87036002],
                        [ 16.78999329,   7.5       ,   3.39222002]] ) +array([x_shift,0.,0.] ) )*Angstrom

Actually it was slight mistake .There should be numpy.array instead of array
No need for "from numpy import array" or "from numpy import *"
I got script work