Messages

1

General Questions and Answers / Re: a paradox about Conductance of Si and Cu

« on: February 22, 2012, 09:13 »

tnx Anders and Nordland for you good responses.

2

General Questions and Answers / Re: a paradox about Conductance of Si and Cu

« on: February 22, 2012, 08:30 »

It is also very important to understand there is a difference between a Cu atom and Cu crystal. And the same goes for Silicon.

Take my favorite element carbon. As a single atom it has a huge homo-lumo gap. As a atomic wire it can be metallic. As graphene it is semi-metallic, as nanotubes it can be semiconducting.

So in short the behavior of materials can rarely be derived from a single atom, as the interaction with other atoms is most of the physics.

It means that the roles may be different for atomic structures when we have only one atom, so my question: when we say that Silicon is semiconductor, it means that bulk silicon is semiconductor? and may be the single atom is not... is it true? 

3

General Questions and Answers / Re: a paradox about Conductance of Si and Cu

« on: February 21, 2012, 15:28 »

Thank you so much for your nice response. And another question: do you think there are any difference between conductance results of a defined system in 2008 version and 2011 version?

4

General Questions and Answers / Re: a paradox about Conductance of Si and Cu

« on: January 29, 2012, 08:54 »

I have attached the related system for Si, electrode length is 1.8 and mesh cut off=100, K-points=100 and other default parameters.
you can change the central region width for example from 8 to 10 and then with the same conditions make the computations again for Cu, you'll see Si conductivity would be greater!!! Please kindly someone do it, I want to know that this error is inside me or not.

tnx

5

General Questions and Answers / Re: a paradox about Conductance of Si and Cu

« on: January 28, 2012, 17:16 »

I located just a Si atom and a Cu atom between electrodes, then I tried different distances. I set the system in the contact mode in minimum distance between Gold and related atom, then the distances were increased symmetrically in both side. I tested the system for about 20 different cases and in all of the Si conductance was higher than Cu!!! 

6

General Questions and Answers / a paradox about Conductance of Si and Cu

« on: January 28, 2012, 16:11 »

Dear all

I calculated the conductance of Si and Cu atoms in equal conditions, but the conductance of Si was greater than Si. The electrodes were Gold linear electrodes.
Cu atom is metal with a great conductivity but Si is semiconductor or semi metal, then why the G value for Si is higher?

7

General Questions and Answers / finding the desired conductance among a list

« on: December 13, 2011, 15:25 »

Dear all

I calculated the conductance of a molecule in different distances from the electrodes. I put the molecule in a close distance to electrodes and then the distance between electrodes and molecule is increased. So we have a conductance for each defined distance, how can I find the desired conductance related to this molecule among this list?

tnx

8

General Questions and Answers / Optimization of the molecule with or without electrodes

« on: August 18, 2011, 08:22 »

I have a molecule with 2 atoms of gold in right and left of it. I want to optimize the distance between gold atoms and molecule, what should I do?
I put the gold atoms in an arbitrary distance near the molecule but after optimization the construction was changed in some atoms of the molecule. Should the electrodes be in the optimization or the cell is enough?

9

General Questions and Answers / Re: error with drag molecule configuration into costum/ molecular junction

« on: July 21, 2011, 08:03 »

In the custom/molecular junction for example we define a 2*2 electrode [Au(100)] and minimum length of 4, now; if the molecule's vertical length be more than the vertical length of electrode, the configuration of molecule would be changed. In this case, if I calculate the quantum conductance(G) of the mentioned molecule, whether the results would be correct or not?

10

General Questions and Answers / Re: error with drag molecule configuration into costum/ molecular junction

« on: July 14, 2011, 08:27 »

Thank you, I got it. And how the distance between electrodes in ATK can be defined?
whether that is the C vector measure when we define the central region?

11

General Questions and Answers / Re: calculating the conductance of a molecule

« on: July 13, 2011, 18:26 »

I have calculated the HOMO and LUMO of the attached molecule, please take a look on it and kindly write the values to me, I wanna see that the results that I have calculated is same with yours.
tnx

12

General Questions and Answers / Re: error with drag molecule configuration into costum/ molecular junction

« on: July 13, 2011, 18:18 »

Dear Dr. Blom
Is it possible to have an non-alternating device? in a way that atoms in electrodes be independent than central region. some times when the central region width be small, a portion of the central molecule would be appear in the electrodes!!! 

13

General Questions and Answers / Re: error with drag molecule configuration into costum/ molecular junction

« on: July 11, 2011, 07:57 »

Dear Dr. Blom, thank you for your excellent responses. yes, I've tried the builder in VNL, in builder I can not have the molecule in central region with gold electrode in two side (device form). First we put the gold, then we define the lattice and number of repetitions for central region and afterward we can transmit it to device mode. when I put Adamantane as my molecule, the electrodes also changes from gold to Adamantane. The final device would be two electrode (Adamantane) and an ADM molecule between them!!!
I think it would be solved by python code, I haven't already written a python code but I start it and I'll come back 

Best

14

General Questions and Answers / Re: error with drag molecule configuration into costum/ molecular junction

« on: July 10, 2011, 18:33 »

I want to have a two electrode system like attached figure. In molecular junction/custom, the width of central region can not be determined by user! I am making effort to put the Adamantane molecule in the central region between two electrodes system ( 2*2 and 1*1) , then compare the conductance of molecule for this two state. on the other hand I have two value of central region, 9 and 11 Ang.
Can I do it in custom?

15

General Questions and Answers / calculating the conductance of a molecule

« on: July 9, 2011, 18:51 »

Hi
I am a new user with VNL/ATK, for calculating the conductance of a molecule between 2 probe, what should I do?