Messages

1

General Questions and Answers / Purpose of Electrode Extension ???

« on: January 10, 2019, 12:44 »

Dear QW team,

When we build a two probe device... The device consists of electrode regions and electrode extension regions.

What is the purpose of this Electrode extension region ??
Is it to mitigate the effect of a practical contact ?

Please clarify.

2

General Questions and Answers / Re: Different band structure of Graphene for 6 repetitions

« on: August 20, 2018, 19:13 »

Yes Dr. Petr... You are right.
I overlooked the bandstructure for 3*3 repetition.

Thank you so much for the clarification.

3

General Questions and Answers / Re: Different band structure of Graphene for 6 repetitions

« on: August 20, 2018, 08:13 »

Dear Experts and Quantumwise Staff,

May I request you to please take few minutes towards my query please.

4

General Questions and Answers / Different band structure of Graphene for 6 repetitions

« on: August 18, 2018, 08:21 »

Dear Experts,

I was calculating the band structure of graphene by repeating the hexagonal primitive cell for testing purposes.
I repeated the hexagonal primitive cell 2, 3 , 4, 5, 6, 7 and 8 times, respectively.
I have received typical graphene band structure with Dirac point at the 'K' point of brillouin zone for 2, 3, 4, 5, 7, 8 repetition cases.
However, the 6 times repetition case shows a different band structure with Dirac point at 'G' point. (The images are attached below).

Why the band structure is different only for 6 repetitions case ?
Let us say it is a result of folded bands and shrinked brilllouin zone due to the repetition of supercell. Then why we are getting the typical band structure (having dirac point at 'k' point) for 7 and 8 repetition cases

Please explain.
Awaiting your suggestions.

5

General Questions and Answers / Re: pH value - molecular dynamics

« on: December 5, 2017, 19:30 »

Dear Dr. Ulrik,

I want to check the dispersion behaviour of graphene flakes in an aqueous solution at different pH levels.
I want to use "Molecular Dynamics" incorporated in ATK.
All I could not get is, How to vary the pH levels of aqueous solution in ATK-VNL

Awaiting your reply,
thank you so much.

6

General Questions and Answers / pH value - molecular dynamics

« on: December 4, 2017, 15:20 »

Dear Experts,

I am eager to know if there is any way to adjust the pH value of solution inside the supercell, while performing molecular dynamics.

Thanks.

7

General Questions and Answers / Re: Why am I getting a small bandgap in density of states of graphene?

« on: April 10, 2017, 11:52 »

Ok...
thank you Dr. petr

8

General Questions and Answers / Re: Why am I getting a small bandgap in density of states of graphene?

« on: April 10, 2017, 10:58 »

Dear Dr. Daniel,
   The code u suggested produces no different plot than the VNL. I request you, to verify your plot for an energy range of -1eV to 1ev, coz the very small band gap can't be seen in a wide energy window.

Dear Dr.Petr,
I used the version 2014.3.
Yes, the 129*129 k-grid worked for me, while the 27*27 didn't. However, the plot produced from 129*129 grid is little uncomfortable to deal with. please find the attached DOS for 129*129 grid over a wide energy range and its zoomed version. 

9

General Questions and Answers / Re: Why am I getting a small bandgap in density of states of graphene?

« on: April 7, 2017, 12:36 »

Dear sir,

I went through the appendix of the article.

I tried several k-points and combinations, but the problem still exists.
I also used dense 288*288*1 k-points for both SCF and DOS in the code attached below, still I am getting a small band gap when I zoomed the plot to -1 to 1 eV range.

The code and the plot are attached below.

Please suggest... I am exhausted from my side.

10

General Questions and Answers / Re: Why am I getting a small bandgap in density of states of graphene?

« on: March 24, 2017, 16:27 »

It's easy to say someone to refer to some paper. Well, its a good thing and I appreciate your suggestion.

However, to get the zero band gap in the DOS, all i need to do finally will be definitely changing the parameters or theory. I have taken the converged parameters for the calculation, still I am getting the issue. You should have pointed out the problem and convey where the issue was. 

Even if i read the whole paper u referred, I won't be able to know what values of k-points and mess cutoff i have to choose to get the accurate result.
 I appreciate your suggestion (reference paper) and I am on it, but plz try to identify the issue instead of skipping it.

11

General Questions and Answers / Re: Why am I getting a small bandgap in density of states of graphene?

« on: March 24, 2017, 14:23 »

I have increased the k-points to 24*24*1.
and considered 40 bands above the fermi level.

Still, the problem persists.

12

General Questions and Answers / Why am I getting a small bandgap in density of states of graphene?

« on: March 24, 2017, 13:39 »

Dear QW experts,

I have test simulated graphene (2 atoms) for the band gap and DOS. I observed a small band gap from the density of states plot.

I have attached the python script and the obtained DOS plot for your reference.

Please point, where am I doing wrong?

13

General Questions and Answers / Re: Calculating Quantum Capacitance

« on: March 8, 2017, 07:53 »

Thank you very much Dr. petr and Dr. Zh for the papers.
I will go through these papers and get back if there is any issue.

thank you.

14

General Questions and Answers / Calculating Quantum Capacitance

« on: March 7, 2017, 14:22 »

How to calculate Quantum capacitance of a graphene sheet using ATK?
Can someone help me with this, plzz.

Thank you very much for your time.

15

General Questions and Answers / Re: problem displaying Bandstructure of Graphene: VNL as QE GUI

« on: January 5, 2017, 12:01 »

Yes sir... the system has been setup using VNL only.

I am using latest version QE 6.0.

The VNL version is 2016.3.