Messages

181

General Questions and Answers / Re: bilayer graphene

« on: December 23, 2016, 10:00 »

You can still use the graphene unit cell.

Once you have the supercell go to Bulk Tools -> Supercell and transform the cell to "Base-Centered Orthorombic".
Then, go to Bulk Tools -> Swap Axes and swap the axes so that C is the direction normal to the graphene plane.

Then you should have a unit cell that is suitable for transport calculations    

182

General Questions and Answers / Re: bilayer graphene

« on: December 22, 2016, 15:05 »

Check this tutorial:
http://docs.quantumwise.com/tutorials/opening_a_band_gap/opening_a_band_gap.html

183

General Questions and Answers / Re: VNL crashes when working in Builder

« on: December 22, 2016, 10:08 »

It could be possible for you to ask for the system info from the about box. You can start VNL, so it should be possible to do it. The about box is located in the Help menu at the top of the VNL main window.

184

General Questions and Answers / Re: ATK Classical

« on: December 22, 2016, 09:55 »

No as Petr says with classical potential you can only do phonon calculation so maybe you can be interested in checking the phonon band structure.

185

General Questions and Answers / Re: Potential for interface

« on: December 19, 2016, 12:04 »

Dear Berna,

thank you for sharing the details of your issue with the ATK community.

Classical potentials such as those you want to used are not only used in the Interface Builder, which I guess from your question is the VNL plugin you are actually using. They are actually mostly used in ATK as a calculator and as such they can be selected in the Script Generator.

Unfortunately, if the shift-surface button is not active, it means that there is no classical potential in ATK available   
for your desired combination of elements (in this case, Zn, O, Au). If you have your own potential, you can actually implement it as specified in: http://docs.quantumwise.com/tutorials/combining_potentials/combining_potentials.html.

Another, probably easier option is to shift the surface manually and set the distance using chemical intuition: for most system, bonding distances are in the range 2.0-3.5 Angstrom, so setting a distance in this range will probably provide a reasonable starting guess. Then, you can optimize the structure of the interface using DFT, which is also implemented in ATK. Although I am not an expert, I am aware that the ZnO-Au interface has been studied a lot, so I think you can also check the literature to obtain reasonable estimates for the correct binding distance.

Regards,
Daniele.

186

General Questions and Answers / Re: Extended Huckel Device calculation gets extremely slow

« on: December 12, 2016, 16:30 »

I guess the first two SCF cycles are the electrode calculations, and the "slow" one is the actual device. The device is probably 
larger than the two electrodes, so it makes sense that the device calculation is slower.

We could say something more if you send the input and output scripts of the calculation.

Regards,
Daniele.

187

General Questions and Answers / Re: Germanium nanowire

« on: December 8, 2016, 13:28 »

Hello Azi,

I looked a little bit into the problem. The main issue there is that the band gap calculated using the Huckel method is very large (around 5 eV), whereas the band gap calculated using DFT is much smaller (around 1 eV).

From a numerical point of view, at given temperature (in your calculations, the electronic temperature is k_B*T = 0.025 eV) it becomes increasingly difficult to resolve the position of the Fermi level in the gap when the energy gap increases. So, if you want the Fermi level positioned correctly in the nanowire calculated using Huckel, you have to increase the temperature.

Regards,
Daniele.

188

General Questions and Answers / Re: Germanium nanowire

« on: December 7, 2016, 15:54 »

Where should it be? The Fermi energy lies in the middle of the gap only for bulk non-doped semiconductors.
I also see you are using a semiempirical method to describe your structure. Are you sure that the parametrization works well for your system? Did you check it against DFT ?

Regards,
Daniele.

189

General Questions and Answers / Re: Curie temperature

« on: November 28, 2016, 09:37 »

Unfortunately, ATK 2011 is not supported anymore.

190

General Questions and Answers / Re: interlayer distance in classical potential

« on: November 28, 2016, 09:16 »

Apart from the calculator details the rest of an ATK python script should be the same independently on the whether you are using DFT or classical potentials. So you can use the same procedure you have used with DFT.

191

General Questions and Answers / Re: Spin Orientation

« on: November 23, 2016, 08:51 »

You have to be more specific in your question, e.g. which type of analysis? To see what?

192

General Questions and Answers / Re: total energy for hetro structure

« on: November 23, 2016, 08:50 »

In DFT the absolute value of the total energy does not have physical meaning, only differences between total energies have physical meaning.

It is possible to do the E vs. d curve in a single run by editing the script in a python code, but I strongly suggest you to avoid it if you don't know what you are doing. It is safer to do it in separate calculations.

193

General Questions and Answers / Re: Device configuration for stacked 2D materials

« on: November 17, 2016, 09:05 »

If you attach in input file for the structure I can have a look 

194

General Questions and Answers / Re: Align ABC with XYZ for stanene (alpha Tin)

« on: November 16, 2016, 10:05 »

If you have a strategy that worked for graphene, than I would suggest to use it also for stanene, the only thing you have to do is to change the atoms from carbon to Tin, and of course set/calculate the correct lattice constant for the unit cell of the 2D hexagonal structure.

195

General Questions and Answers / Re: Device configuration for stacked 2D materials

« on: November 16, 2016, 09:02 »

Yes, of course, you just have to use the "Device from Bulk" plugin in the builder