Messages

1

General Questions and Answers / Re: Can ATK deal with the spin-dependent interface coupling?

« on: August 3, 2018, 11:34 »

Please provide reference material on how this spin-dependent interface coupling is included in the self energy calculation.

2

General Questions and Answers / Re: methods used for spin transport measurements

« on: May 20, 2015, 17:23 »

Any suggestions ?

3

General Questions and Answers / methods used for spin transport measurements

« on: May 19, 2015, 06:25 »

What method (or methods) is used to perform spin transport in MTJs, particularly interested in knowing

(i) coherent transport models for the spin transport
(ii) and the use of full-wave numerical simulation in spin transport.
(iii) how the doping is taken into account in  modeling spin transport (i.e., coherent transport in presence of doping in graphene)

Thanks in advance.

4

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

« on: July 8, 2011, 09:01 »

I have a 5X5X5 Au electrodes cell and a (8, 0) CNT in the central region.

How many K-points are required in X-Y ?
What size of electrode unit cell is considered large so as to use 1X1 k-point in X-Y ?

best regards,

5

General Questions and Answers / Re: BandGap from plot

« on: November 29, 2010, 15:11 »

Thank you sir!

6

General Questions and Answers / BandGap from plot

« on: November 29, 2010, 14:45 »

The script written by Nordland, in the link which you mentioned above fails for semiconducting material, I tried that script and got wrong results for few configurations, while also got correct results for few systems.

can't we use energy band plot to find band gap?

7

General Questions and Answers / BandGap from plot

« on: November 29, 2010, 14:37 »

Dear Sir,

Is it possible to find band gap and HOMO/LUMO from Energy Bands plot using

Code

calculateEnergyBands(scf,k)

?

please see the attached energy band plot

8

General Questions and Answers / Re: some questions about the geometric optimization

« on: November 17, 2010, 08:00 »

Dear Sir,

Can you give a reference of "Steepest descent algorithm based on a damped velocity-Verlet MD algorithm", which is used by ATK.

9

General Questions and Answers / Re: KeyError

« on: November 15, 2010, 10:27 »

Dear Sir,

I was trying to obtain the atoms in the central region for nanotube using the below mentioned code:

Code

from ATK.TwoProbe import *
from displayCentralRegion import displayCentralRegionAtoms

vnl_file=VNLFile("CNT.vnl")
atomic_configuration_dict = vnl_file.readAtomicConfigurations()
atomic_configuration = atomic_configuration_dict["twoprobe_configuration"]
displayCentralRegionAtoms(atomic_configuration)
      

then i tried using code mentioned below, but got errors:

Code

...
vnlfile=VNLFile("file.vnl")
configs=vnlfile.readAtomicConfigurations()
twoprobe_config=configs[configs.keys()[0]]

I get:

Code

  File "Li_SW15_2-Trans.Spec.py", line 9, in ?
    twoprobe_config=configs[configs.keys()[0]]
IndexError: list index out of range
Traceback (most recent call last):

And, when I try to get the configuration name using

Code

...
vnlfile=VNLFile("file.vnl")
configs=vnlfile.readAtomicConfigurations()
print configs.keys()

I get only []

How do i obtain the central region atoms with periodic_atom_configuration such as in nanotubes?

10

General Questions and Answers / Re: Nanotube with Cu electrodes

« on: October 20, 2010, 13:29 »

Dear Sir,

How do we provide electrode connection to metal-semiconductor CNT heterojunctions?

From [APPLIED PHYSICS LETTERS 96, 102108 (2010)], the separation distance between the a straight wire CNT and Cu electrode is 1.85 Å for end-contact and 1.20 Å for side-contact. These distances were determined by minimizing the interaction energy of the system to ensure a stable configuration.

Please look at the attached picture, the tube angle is troubling.

The atoms at the end of tube don't have same Z-coordinate.

regards,

11

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

« on: October 18, 2010, 12:45 »

Dear Sir,

I use K- points (1,1,100) for single wall CNT.

What will be the suitable number for a Double Wall CNT (DWCNT)?

12

General Questions and Answers / Re: Nanotube with Cu electrodes

« on: October 18, 2010, 11:54 »

Thank you very much sir for the discussion.

regards,

13

General Questions and Answers / Re: Nanotube with Cu electrodes

« on: October 18, 2010, 10:13 »

Sorry, I wanted to say transmission near by 0 eV is zero.

Sir, please look at the pictures that are taken from "Appl. Phys. Lett. 94, 183506 (2009)"

In the top figure, the transmission width is wide (no transmission) in energy range (near by 0 eV)

In the bottom two pictures, there is transmission at 0 eV, which shows semiconductor-to-metal transition.

14

General Questions and Answers / Re: Nanotube with Cu electrodes

« on: October 18, 2010, 09:42 »

I have read that for semiconductor-to-metal transition, the transmission spectra should be above the Fermi level (0 eV).

But in this case, the transmisson spectra width widens at the Fermi level (at 2 volts bias), though the current obtained is high (micro-amperes). There are peaks observed in T (E) which could be the possible reason of high current.

So can we still say that there is a semiconductor-to-metal  transition?

15

General Questions and Answers / Re: Nanotube with Cu electrodes

« on: October 18, 2010, 09:21 »

Thank you for clearing my doubt, this is certainly informative that semiconducting leads will give no current.

I used a semiconducting lead with a semiconducting central region and found current of the order of 10^-10 amperes at 2 volts.

Then i radially compressed the central region and used radially compressed semiconducting electrodes similar to central region, and found current of the order of 10^-6 amperes at 2 volts. Which may be due to semiconductor to metal transition, a common phenomenon observed in deformed CNTs. In case of lower bias voltages also there was an increase in current of the same order.

My question is that, Can't we comment on the conductivity of different semiconducting nanotube structures using semiconducting electrodes ?

Of course, the current obtained will be higher in case of metallic electrodes,  and the ratio by which current increases may be equally valid for all CNT structures.