Messages

1126

General Questions and Answers / Re: Bloch-state velocity

« on: March 12, 2017, 20:47 »

The Bloch-state velocity is given by the first derivative of the electron band energy, E(k), with respect to the electron quasimomentum, k. If you want to calculate the Fermi velocity of graphene, for example, this velocity is then defined as the Bloch-state velocity calculated at the Dirac (conical) point of the graphene band structure, see http://docs.quantumwise.com/manuals/Types/calculateVelocity/calculateVelocity.html.

Another example is a free-electron gas or any material that can be described with the free-electron gas model. The Fermi velocity can then be seen as the Bloch-state velocity calculated as the first derivative of E(k) with respect to k at the Fermi momentum, k=k_F, which is related to the highest occupied electron states, i.e., the states on the Fermi surface given by E(k_F)=E_F, where E_F is the Fermi energy.

I would suggest reading some basic Solid Physics textbook for a better understanding of this issue, e.g.,  Ashcroft & Mermin: Solid State Physics.

1127

General Questions and Answers / Re: electron density

« on: March 12, 2017, 18:20 »

Do you mean the density of electronic states at the edge of the conduction band? Otherwise, what is your definition of  "electron density" at the edge of the conduction band?

1128

General Questions and Answers / Re: post processing analysis

« on: March 12, 2017, 18:13 »

I think there is such an analysis script in the tutorial I mentioned in my previous post. Otherwise, I am not sure that I understand your problem.

1129

General Questions and Answers / Re: post processing analysis

« on: March 11, 2017, 12:48 »

If some analysis option is not available in the VNL, you will have to write an analysis python script. As an example, please have a look at this tutorial on the subject of your interest, http://docs.quantumwise.com/tutorials/youngs_modulus/youngs_modulus.html.

1130

General Questions and Answers / Re: self consistent with SOC

« on: March 11, 2017, 12:06 »

Yes, you may do it in this way. First, do a spin-polarized calculation, and then use it as a starting point for the device calculation with spin-orbit interaction included.

1131

General Questions and Answers / Re: how to set up LDA+U+SOC calculation?

« on: March 9, 2017, 11:52 »

This will not work. The LDA+U+SOC feature has not been implemented in the ATK yet. 

1132

General Questions and Answers / Re: Calculation of thermal conductivity of a graphene layer

« on: March 9, 2017, 10:32 »

You may have a look at our tutorial on the thermal conductance calculations at http://docs.quantumwise.com/tutorials/interfacial_thermal_conductance/interfacial_thermal_conductance.html. There is also our recent webinar video on this topic, posted on youtube, see https://www.youtube.com/playlist?list=PLkOUx2yxHrqxH5szv2HUX0JwqD25Y2Ab8&utm_source=ZohoCampaigns&utm_campaign=Send+links+to+MD+webinars+participants_2017-03-06&utm_medium=email. 

You may also be interested in watching the webinar video on molecular dynamics simulations in the ATK, see https://www.youtube.com/playlist?list=PLkOUx2yxHrqweTQGgrgiH5wC_WlHKwq5i&utm_source=ZohoCampaigns&utm_campaign=Send+links+to+MD+webinars+participants_2017-03-06&utm_medium=email.

1133

Gallery / Re: Pillared Graphene

« on: March 9, 2017, 09:30 »

You may read the paper cited in the original post to find out where these models can be used.

1134

General Questions and Answers / Re: graphene-boron nitride heterobilayer

« on: March 7, 2017, 20:13 »

You can certainly build this structure in this way. There is a vast literature on the topic. I would suggest searching for it to decide on what would be the most realistic structure of such a bilayer, based on experimental and theoretical findings. It might be that the two layers grow on top of each other in different ways, depending on the growth conditions. So, the choice of the structural model depends on the actual goal of your research study of this 2D system.

1135

General Questions and Answers / Re: pseudopotential-basis set

« on: March 7, 2017, 16:36 »

For the sake of consistency, I would stick to one pseudopotential for all the calculations, including geometry optimization.

You may read about pseudopotentials in the ATK at http://docs.quantumwise.com/technicalnotes/atk_pseudo_basis/atk_pseudo_basis.html, as well as following the links and references therein for having even more information on the pseudopotentials.

1136

General Questions and Answers / Re: Calculating Quantum Capacitance

« on: March 7, 2017, 16:27 »

There is no standard feature in the ATK to do this kind of calculation. But I guess you may first calculate the density of states of a graphene sheet in the ATK to then get this capacitance in a post-processing manner.   

1137

General Questions and Answers / Re: pseudopotential-basis set

« on: March 7, 2017, 11:25 »

See the following Forum discussion on this topic: http://quantumwise.com/forum/index.php?topic=3185.0. The ATK version you are using is quite old by now, whereas the tutorials refer to an up-to-date version of ATK.

1138

General Questions and Answers / Re: Adding vacuum in monolayer structure

« on: March 6, 2017, 09:19 »

In the Builder, you should select Bulk Tools -> Lattice Parameters, and then increase the lattice parameter of the WSe2 unit cell in the out-of-plane direction to enlarge the vacuum thickness in between neighboring monolayers of WSe2. 

1139

General Questions and Answers / Re: Can ATK simulate AC response of graphene devices?

« on: March 6, 2017, 09:13 »

The ATK calculates the direct current only, so there is no frequency parameter to be set.

1140

General Questions and Answers / Re: Sabalcore Problem

« on: March 5, 2017, 19:31 »

If you are the only one who is unable to connect to Sabalcore, nobody will reply to your post, so that you will never be able to fix the problem. I would also suggest contacting the QW support, but you then need to provide more detailed information on this error issue.