Messages

1

General Questions and Answers / Difference in density of states for bulk and device density of states

« on: March 19, 2014, 22:35 »

Hi All,
I calculated density of states for a bulk configuration and then used device from bulk to get a device. Then I added some charges on electrode to get a p-i-n structure. I calculated device density of states and found it to be significantly different from bulk DOS.

Can anyone explain why should DOS change significantly from device to bulk configuration?

Thanks

2

General Questions and Answers / Getting text values for projected Hartree potential

« on: March 6, 2014, 01:41 »

Hi,

Once a self consistent calculation is completed, we can project it on x,y,z dimensions. Now can I get the text representation of this projected plot in form of 1D array.

Thanks,
-Arya

3

General Questions and Answers / Skipping variation of potential in X, Y direction

« on: February 18, 2014, 03:34 »

Hi,

Greetings !

In the NEGF formalism (what I understood by reading some papers from S. Datta) we use a eigenspace representation for Hamiltonian in X, Y direction and a real space Hamiltonian representation in transport direction.
This means we need the variation of potential (U) only in transport direction since XY direction are taken care by eigenspace representation.

If my understanding is correct do we have option of not calculating potential variation in XY direction, thus speeding up the calculations.

Of course others might want to see a 3D view of potential but in case one doesn't need; can we skip the X,Y direction and use just the Z direction for NEGF calculations.

Thanks,
-Arya

4

General Questions and Answers / Re: Getting the 'classical' LDOS for a TFET including screening length

« on: February 7, 2014, 01:04 »

Image of LDOS calculated by ATK..

5

General Questions and Answers / Getting the 'classical' LDOS for a TFET including screening length

« on: February 7, 2014, 01:01 »

Hi All,

1. I calculated the LDOS for a GNR small device. To me it looks wierd (VGS = VDS = 0.4V) with -0.9 charge on left electrode and 0.9 cahrge on right electrode. Is my result correct? Have a look at attached .py and png files.

2. ATK calculates LDOS only for central region, this doesn't give us the classical picture of LDOS found in literature. Also one cannot visualize screening length from the central region picture. How can I get the LDOS as shown in 'Literature_LDOS.png' ?

The X axis in LDOS does not correspond to physical dimension of my device in transport direction. Why? I have attached the script I used to generate contour plot.

Thanks,
-Arya

6

General Questions and Answers / Re: K point Sampling

« on: February 5, 2014, 17:58 »

Thanks Dr. Blom !

7

General Questions and Answers / Re: MoS2 transmission and the gate voltage

« on: February 3, 2014, 16:17 »

Thanks Anders! That does makes sense

8

General Questions and Answers / Re: MoS2 transmission and the gate voltage

« on: February 2, 2014, 01:18 »

Thanks Anders,

Here is another question. I have attached three images of LDDOS for a GNR FET:

lddos_nogate_nocharge.png: Is for a GNR-device without any gate or bias. (This curve seems good)
lddos_pin.png: Is for a p-i-n structure with GNR no bias (charges are added to both electrodes) (We can see the slope in LDDOS as expected)
lddos_with_gate_volatge: Is the same structure with gate at -1V without any charges on electrode

Now in the third figure we see the conduction band moving up due to gate voltage. Why is the valence band not effected? Shouldn't it move up as well?

I in fact tried to have second gate with 0V but things didn't change.

Thanks in advance
-Arya

9

General Questions and Answers / K point Sampling

« on: February 1, 2014, 03:29 »

Hi All,

Every time I set up any structure I have no idea what k point sampling to use. Can anyone shed light on what exactly is this k point sampling and how do we guess what value to use?

Thanks,
-Arya

10

General Questions and Answers / Re: MoS2 transmission and the gate voltage

« on: February 1, 2014, 03:26 »

Sir,

Tutorials on graphene FETs do not add any gate below with 0V. Why do we require extra gate for MOS2?

11

General Questions and Answers / Re: MOS2 bandstructure

« on: December 16, 2013, 13:28 »

Thanks Dr Anders and Shinji Usui, I will try your script.

-Arya

12

General Questions and Answers / Re: MOS2 bandstructure

« on: December 15, 2013, 16:01 »

I am using 13.8. I don't see the reason why am I not getting correct results. As far as parameters are concerned all we need to chose is k space sampling (which is 1,3,3 for me for Slater Koster) and Brillioun zone route.

The problem is I want to know how to decide what parameters etc to use so that if I wish to calculate bandstruture for a new material I shouldn't rely on tutorials.

Thanks,
-Arya

13

General Questions and Answers / Re: Electrostatic difference potential and basic parameters

« on: December 15, 2013, 04:44 »

Thanks Dr. Anders.

The choice of representation in literature is to choose eigenstate representation for x-y direction and real space representation for z direction. With this representation we wont be able to look at electron density/ Electrostatic difference potential in 3D space (correct me if I am wrong).

Can I choose which representation to use in x-y direction?

Thanks,
-Arya


 

14

General Questions and Answers / About self consistent potential

« on: December 15, 2013, 03:58 »

Hi,

I am not very familiar with notations used in Quantumwise manual. But here is what I need, Hamiltonian [H+U] is self consistently solved poisson's equation. How do I plot this U with respect to device length (z direction)? Is U the Hartree potential?

Thanks,
-Arya

15

General Questions and Answers / Re: MOS2 bandstructure

« on: December 15, 2013, 03:41 »

Just a question, is it always necessary to have an orthorhombic unitcell for bandstructure calculation? Why do we prefer orthorhombic cell?

Also the unit cell that I was using (mentioned in above comment of mine), what is wrong with that? For orthorhombic cell we do not get 'K point ' in Brillioun zone route as far as I know.


 
Thanks,
-Arya