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### Topics - Jenny

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1
##### General Questions and Answers / transmission spectrum for nanotube
« on: October 19, 2016, 17:56 »
Hello, everyone.

I found that in the tutorials (http://quantumwise.com/support/tutorials/item/515-isotope-impurity-effect-on-a-single-wall-carbon-nanotube), the electron transmission spectrum has a dip at the Fermi level for carbon nanotube (6,0). However, theoretically the transmission value should be 2, instead of 0.

what is the problem with the tutorial? And how can we get the correct result?

Jenny

2
##### General Questions and Answers / Transmission eigenvalues for one mode larger than 1
« on: July 20, 2016, 21:44 »
Hi, everyone.

When I tried to calculate the transmission eigenvalues at Fermi level for my one-dimensional system, it came out with the result as below. The weird thing is that I got the first four channels that have eigenvalues larger than 1. I thought the range for the eigenvalues should be 0 to 1. Why would this happen?

+------------------------------------------------------------------------------+
| Transmission Eigenvalues Report                                              |
| ---------------------------------------------------------------------------- |
| Left electrode Fermi level   = -4.316601e+00 eV                              |
| Right electrode Fermi level  = -4.316601e+00 eV                              |
| Energy zero                  = -4.316601e+00 eV                              |
| Energy                       =  0.000000e+00 eV                              |
| ---------------------------------------------------------------------------- |
| Number of transmission modes = 49                                            |
+------------------------------------------------------------------------------+
Eigenvalues (Up):
1.376425e+00
1.142384e+00
1.046487e+00
1.003812e+00
9.181272e-01
8.580740e-01
8.237050e-01

The parameters I used to do the calculation is like this :
energy=0*eV,
k_point=[0, 0],
energy_zero_parameter=AverageFermiLevel,

3
##### General Questions and Answers / how to plot transmission coefficient as a function of energy and bias
« on: July 5, 2016, 23:34 »
Hi, everyone.

I found the chart of transmission coefficient as a function of energy and bias in the link below:
http://quantumwise.com/publications/tutorials/item/506-linear-response-current-how-to-compute-it-and-why-it-is-often-not-a-good-idea
However, the link seems doesn't work now. I tried to google the key words, but nothing came out.

I'd like to plot transmission coefficient as a function of energy and bias for my own system. Does the ATK have the plug-in function to realize it? If not, is there any available codes I can use to plot it?

Thank you very much.

Jenny

4
##### General Questions and Answers / DFT calculation of a perfect Cu wire
« on: April 7, 2016, 22:17 »
Hi, everyone. I tried to follow the tutorial of a perfect Al wire (https://www.quantumwise.com/documents/manuals/ATK-2008.10/chap.altranseigenchan.html)
And the same method was applied to calculate the optimum distance of a perfect Cu wire and the transmission spectrum of the wire. I've attached my script here.

I found that there are three states at Fermi level for a perfect Cu wire, which indicates that a perfect Cu chain is conductive at zero temperature. However, my professor argued that physically a perfect Cu wire should not be conductive at all because there are no electron sharing. So, was there anything wrong with my calculation? or a perfect Cu wire should be conductive as the result I got?

Thank you very much.

Jenny

5
##### General Questions and Answers / analysis of zero bias result of a two probe device
« on: March 14, 2016, 23:32 »
Hi, everyone.

I read the tutorial on the Au-DTB-Au device and found a question in the part of "Analysis of the zero-bias result".
https://www.quantumwise.com/documents/tutorials/latest/MolecularDevice/index.html/chap.analysis.html

Here, it mentioned that at Energy=2.4eV, T=1.45 when the calculation was performed with k=3*3 and k=21*21 gave T=1.58 at E=2.4eV. However, even with 21*21 mesh, the T value is still smaller than the sum of two dominating eigenvalues which gives a total transmission of 1.645. Does it mean that we need to increase the k-point sampling? Also, for the other two peaks at E=-3eV and E=-1.5eV, the summation of all transmission eigenvalues does not equal to the total transmission value at each energy level. Do we need to find the k mesh which is large enough to get us the summation of all transmission eigenvalues=total transmission value at each energy level?

Thank you very much.

Jenny

6
##### General Questions and Answers / Combining a Tersoff and a Lennard Jones potential
« on: February 10, 2016, 17:27 »
Hi, everyone.

I can not locate the line where the 'C' element definition in the script, even after I set Script Detail to Show Defaults.

So, instead, I correct my script to

potentialSet = Tersoff_C_2010()
mass=12.0107*atomic_mass_unit,
charge=None,
# Sigma and epsilon from Ref [3].
sigma=3.3611*Ang,
epsilon=0.004207*eV))
mass=6.941*atomic_mass_unit,
charge=None,
# Sigma and epsilon from Ref [3].
sigma=0.826*Ang,
epsilon=0.271115*eV))
particleType2='Li',
r_cut=9.0*Ang))
particleType2='Li',
r_cut=9.0*Ang))

calculator = TersoffCalculator(parameters=potentialSet)

However, when I run the script, an error comes up, saying "Tersoff_C_2010 instance has no attribute 'addParticleType' ". So, how could I modify my script to make it work as it suggested in the tutorial?
BTW, I'm using atk-13.8.1 version.

Thank you very much.

Jenny

7
##### General Questions and Answers / k points setting for nanotube Blochstate
« on: January 29, 2016, 20:22 »
Hi, all.

I want to calculate the Blochstate for nanotube at G and Z?
So the k points setting should be (0,0,0) for G and (0,0,0.5) for Z?
If not, what should the k points be?

Thank you very much.

Jenny

8
##### General Questions and Answers / questions regarding to tutorial of Isotope impurity effect on a single-wall carb
« on: September 9, 2015, 17:45 »
Hello, everyone.

I've done as the tutorial suggested. However, I'got the different results from the tutorial.
I noticed that the default electrode length here I got is different from the tutorial. And I've tried to build a device with cnt(6,0) without optimization. The electrode length seems match the numbers in the tutorial. However, the resultant transmission spectrum is still different from that in the tutorial. I don't know why. Can somebody help me with it?
And I've attached the script and its result here.

Thank you.

9
##### General Questions and Answers / mean free path of electrons in metal
« on: July 31, 2015, 21:26 »
Hello, all.

As we know, if the feature size of a system is smaller than it mean free path, there will be elastic scattering for electrons. Then how can we find the value of MEAN FREE PATH here? Is it available here in QuantumWise? Thank you in advance.

Best,

Jenny

10
##### General Questions and Answers / how to calculate fermi energy of a molecule
« on: July 10, 2015, 22:55 »
I've checked the website attached. However, I can make it work. Can anyone give me some advice? I've attached the configuration I'd like to explore here as well.
http://quantumwise.com/documents/manuals/ATK-2008.10/ref.calculatefermienergy.html

11
##### General Questions and Answers / singular value decompostion failed
« on: June 18, 2015, 21:35 »
Hi, all.

I met a problem when I conducted the calculation with bias between two electrodes in the device. Parallel calculation was running with five computers. The error was running as follow:
*** Back Engine Exception : Singular value decomposition failed
*** Location of Exception: mathutils.cpp:870

This application has requested the Runtime to terminate it in an unusual way.
*** Back Engine Exception : Singular value decomposition failed
*** Location of Exception: mathutils.cpp:870

This application has requested the Runtime to terminate it in an unusual way.

The script I used is attached here. Can anyone give me a help on this?

Thank you very much.

Jenny

12
##### General Questions and Answers / mulliken population problem
« on: April 24, 2015, 00:38 »
Hello, all.

I've built a device which attached here. When I tried to analyze its mulliken population of Al atoms and C atoms, it was found that Al atoms lost some amount (1.59) of electrons to C atoms (-1.678) which could not be right. I know that the mulliken population given here is a numerical result of the calculation, however, the electron transfer from Al to C is still not reasonable here. So, what might the problem be in my device? Thank you very much.

Jenny

13
##### General Questions and Answers / Optimization geometry at different electron temperature
« on: February 17, 2015, 00:59 »
Dear all,

recently, I tried to get an optimized unit cell configuration at different temperature. However, when I set the electron temperature at different temperature (ex: room temperature 300K, low temperature 50K, high temperature 400K), the optimized unit cells have the same configuration which doesn't match my expectation. I applied DFT method here and attached the script I used.
Please give me an explanation or any reference for the explanation.

Jenny.

14
##### General Questions and Answers / self-energy probelm
« on: December 15, 2014, 21:34 »
Hi, all.

I used ATk-13.8.1 to do a calculation of a molecular with two electrodes device. And I found that NEGF was applied here which the self-energy would be chosen to calculation the transmission property of the system.

Would you please explain to me the different matrix of the three self-energy used here?
Recursion
Krylov
Direct

And under what condition, should we use the different self-energy?

Jenny

15
##### General Questions and Answers / how to build a metal nanowire
« on: October 31, 2014, 21:38 »
Hi, all.

Recently, I'd like to build a metal nanowire,and study its electronic properties. Is it possible? If so, would anyone give me some suggestion on "how to build the new geometry"?