Messages

1

General Questions and Answers / Re: Gate voltage calculations in ATK

« on: April 25, 2016, 10:54 »

I meant gate in the middle, yes, I was talking about the effect of gate as an electrostatic source.
Can you please provide me some details as I need to use it for some analysis ?
I want to know how exactly the hamiltonian is modified, in particular, how the position of the gate influences the current ?

Thanks
kanna

2

General Questions and Answers / Gate voltage calculations in ATK

« on: April 22, 2016, 14:23 »

Dear QuantumWise Staff,

Can you please provide more details about how three terminal calculations are done in ATK ?
Is this published or documented somewhere ?

Thanks
Kanna

3

General Questions and Answers / Re: Regarding Graphene Device Tutorial (zigzag-armchair-zigzag)

« on: April 18, 2016, 11:02 »

Thanks Jess.

4

General Questions and Answers / Re: Regarding Graphene Device Tutorial (zigzag-armchair-zigzag)

« on: April 17, 2016, 11:52 »

Hi Jess,
Just a clarification.
From what I understand the ElectronDifferenceDensity refers to the distribution of density along the C direction, and since we find that there is a finite spacing between the atoms we find an oscillatory behavior in the middle part of the plot. But on a more fundamental level is this oscillatory behavior due to difference between the self consistent value which is the output of the NEGF converged solution and the superposition of atomic valence densities which are decaying exponentially (so the charge is zero away from the ion centre while the Density from NEGF is not necessarily zero since it dies down slower)?
Also on another note: to study the effect of bias on a device (say 1V) : we need ElectrostaticDifferencePotential(at 2V) - ElectrostaticDifferencePotential(at 1V). Am I correct in my understanding ?

Thanks
Kanna

5

General Questions and Answers / Re: noise calculation

« on: March 10, 2016, 08:39 »

1/f noise depends on the material properties which I think is not possible under NEGF.
Will thermal noise (which is modeled by a resistor) be captured in the newly added electron phonon interaction feature ?

Thanks
Sathyajit

6

General Questions and Answers / noise calculation

« on: March 3, 2016, 20:11 »

Hi,
Is there a way to calculate noise in a device with ATK ?

Regards
Kanna

7

General Questions and Answers / Re: Exporting images in eps, in ATK 11.2.3

« on: January 28, 2016, 13:56 »

Thanks.

8

General Questions and Answers / Re: Exporting images in eps, in ATK 11.2.3

« on: January 28, 2016, 06:37 »

Hi,

Even though the dialog in the builder shows an option for structure to be exported in .svg/.svgz format we are unable to save it in that format. Any solution for this ?

Is it possible to use a piece of python code in the structure definition of .py file to get the image of the structure in .eps/svg/svgz/any vector graphics format ?

Thanks
kanna

9

General Questions and Answers / Re: calculation of gate oxide capacitance

« on: January 21, 2016, 10:46 »

Hi,
I want to calculate gate-source capacitance for a given gate bias. I understand the part about setting up a device structure, but how do I get the charge transfer ?

Thanks
kanna

10

General Questions and Answers / Re: understanding memory consumption

« on: January 20, 2016, 10:25 »

Thanks Jess,
With reference to my above questions,
-Reducing cell size means that I need to have more k-points for the simulation so that I get good accuracy of results, even reducing the mesh cut-off reduces accuracy.
Is there a thumb rule for these parameters ?

Summarizing, to reduce memory consumption , the options are:
1. reduce k point sampling along c direction
2. reducing density mesh cutoff
3. basis set (DZP, SZP)
4. Does exchange correlation significantly affect memory / CPU time ?

11

General Questions and Answers / understanding memory consumption

« on: January 20, 2016, 10:15 »

Hi,

In the log

| Size of dense matrices = 10516 x 10516 [1687 MB per matrix]                  |

|                                                                              |
| Storage of orbitals in real space is disabled.                               |
| Enabling storage requires an additional   607 MB.                            |
|                                                                              |
+------------------------------------------------------------------------------+
+------------------------------------------------------------------------------+
|                                                                              |
| Real space grid sampling is (61, 111, 773) in a, b, and c directions.        |
|                                                                              |
+------------------------------------------------------------------------------+
+------------------------------------------------------------------------------+
|                                                                              |
| Storage of atomic core grids requires    39 MB per grid                      |
|                                                                              |
+------------------------------------------------------------------------------+

• I think the dense matrices are formed from the sparse matrices in the calculation , but how many such dense matrices are used ? In my simulation each mpi thread takes 10.9 GB of memory.
• How is the real space sampling controlled ? I am guessing it is related to the resolution of k points we give in the calculation , am I correct to assume this ?
• How many atomic core grids are present ? Is this the number of atoms in the structure * 39MB in this case ?Does this depend on the basis set (SZP/DZP) and exchange correlation alone ?[\li]
  

Thanks
kanna

12

General Questions and Answers / calculation of gate oxide capacitance

« on: January 19, 2016, 15:46 »

Can we calculate the gate oxide capacitance of a mosfet with the tutorial given in
http://quantumwise.com/publications/tutorials/item/511-calculation-of-atomic-scale-capacitance ?

13

General Questions and Answers / Re: cluster configuration

« on: January 19, 2016, 15:10 »

I just got a bit confused, when we use mpiexec -n X, X is the number of threads and each thread corresponds to 1 atkslave license (Is this correct ?)
Please take a look at
http://ark.intel.com/products/83361/Intel-Xeon-Processor-E5-2667-v3-20M-Cache-3_20-GHz

and let me know if we can use only mpiexec -n 8 for this processor (this means 8 atkslave licenses ?)

Thanks
kanna

14

General Questions and Answers / Re: cluster configuration

« on: January 19, 2016, 14:38 »

Apologies for my ignorance.
If we buy a server with 2 processors (each with 16 threads, connected by QPI as shown in the attached chipset diagram), so that in total we have 32 threads in the server
Then will mpiexec -n 16 , it parallelize into the 2 processors perfectly (where each processor has 16 threads) ?

Thanks
kanna

15

General Questions and Answers / Re: cluster configuration

« on: January 19, 2016, 06:59 »

Dear Anders,

Is there a limitation on the bus speed which connects main memory and CPU cluster ?
Is it advisable to have two CPU clusters connecting to the same memory or single CPU cluster connecting to the main memory ?
Also do we need to have different bus for each cluster ?