Topics

1

Installation and License Questions / question about VNL license for academic user

« on: March 17, 2016, 10:45 »

Dear VNL support team,

It was really good news to use free VNL for academic user.
I installed VNL (2015) and got the free VNL license in Feb 17. But now (March 17) when I opened the VNL , it said license was expired.

As I know of, VNL license is perpetual and unlimited.
Why does free VNL license be expired only after one month?

It is written in my license file,  "# License type          : Permanent"
but in the C:\Users\username\.quantumwise\licenses\quantum_15.0.lic, "# Demo license for ATK 15, valid until 2016-03-16"

Why the two due-dates are so different?

Thank you in advance.

2

General Questions and Answers / Is the experimental conductance of graphene comparable with ATK results?

« on: May 5, 2015, 05:48 »

Dear ATK team

I wonder if the conductance of graphene calculated in ATK results can be comparable with an experimental value.

I already know most of the measured conductance of graphene reflects incoherent scattering, thus it can not comparable with ATK results.

But, how about the case in the paper "Phase-coherent transport in graphene quantum billards" (Science, 2007, 317, 1530-1533). I think under this measurement condition, the comparison between experiment and calculation can make sense.

I wonder this comparision can be possible.

Attached is the paper titled "Phase-coherent transport in graphene quantum billards"

Thank you in advance.

3

Installation and License Questions / vnl error to visualize

« on: March 30, 2015, 19:35 »

Dear ATK team,

I have the floating license in my linux server.
I wonder if there is a way to apply this license of linux server to my own computer (windows 8).
This is because there is a problem to visualize my models by ATK running in linux server (as an attached picture)
I think it is because of the low performances of graphic driver/card in linux server, but upgrading the graphic driver/card  is actually impossible.


Thank you in advance your reply.

4

General Questions and Answers / default k-points integration methods?

« on: March 2, 2015, 15:03 »

Dear ATK team,

Based on my knowledge, there will be k-point integration (as gaussian smearing or tetrahedron methods) in every SCF steps in periodic system calculation.

When we calculate DOS by different k-point integration schemes (gaussian smearing or tetrahedron method), we can use .nc file  of the previous SCF results.
I think if DOS by certain k-point integration scheme should be meaningful, the SCF calculations also performed by the same integration scheme.

However, I don't know what integration scheme operate during SCF calculations which occur far before the DOS calculations.

Thus, I'd like to know what is the default k-point integration method during SCF calculations in ATK.

Thank you in advance for your answers.

5

General Questions and Answers / How to get Contact Resistance in ATK

« on: December 15, 2014, 14:15 »

Dear ATK team,

I have reproduced a recent published paper of Gao et al. (APL Materials, 2, 056105 (2014),  http://dx.doi.org/10.1063/1.4876635)

They calculated contact resistance by the ATK code, as shown in eq. (1), I wonder how to get the contact resistance in ATK code.

I cannot find exact contact resistance but the Transmission coefficient.

Is the transmission coefficient related with the Contact resistance?

And another question is how to figure out the ATK code the contact resistance at 0 V bias.

To my knowledge, dI/dV shows conductance after I-V calculation.

Does the contact resistance mean the dI/dV value at 0 V after successive bias calculation?

If so, I'd like to know how much interval bias is resonable to calculation dI/dV.


Thank you in advance for your answers.

6

General Questions and Answers / polarization quantum

« on: April 3, 2014, 16:21 »

Dear ATK team,

After I calculated 'polarization', I got several polarization values.
Among them, I understood pi(ionic), pe(electronic), Pt(pi+pe), and total fractional and cartesian polarizations.
But I cannot understood 'polarization quantum'. It has same unit C/m^2 as the total cartesian polarization, but the value(order of magnitude) are totally different.
I wonder what is the difference between total cartesian polarization and polarization quantum, and what is the real polarization value which can be comparable with experimental data.

Thank you for your answer in advance.

7

General Questions and Answers / Polarzation, kpoint grid set

« on: March 24, 2014, 07:36 »

Dear ATK team,

I tried to calculate polarization which using Berry phase calculation.
Users only can put k-point sampling values in ATK script generator.
As I know, kpoint has typical format as "AxBxC", but in the polarization part of the script generator
there was 3x3 matrix.
At first I put my kpoint values in the  diagonal part, but all other part (off-diagonal terms) to be one.
as " 4  1   1
      1  12  1
      1   1   6 "
After that, I switched the off-terms to be 5, and calculated again.
as " 4  5  5
      5  12 5
      5   5  6 "

The final polarization values are different with respect to each off-diagonal term of kpoint matrix.
I wonder the meaning of off-diagonal term in kpoint 3x3 matrix.

How I should set the kpoints to calculate polarization?

Thank you in advance.