Messages

1

General Questions and Answers / Re: Transmission Eigenvalues revisited

« on: October 15, 2010, 09:53 »

Hi again,

Anders, even when an external voltage is applied, is (kx,ky) conserved? I mean, if the energy is fixed and the fermi levels are different in the contacts, is that assumption  retained?

I think that since the energy difference from E0 to the conduction band minimum is different (kx,ky) should be also different in each contact.

I also think that, as you say, phonon scattering (or other scattering that affects to the energy of the electron) would affect to the energy and thus to (kx,ky) but it is not the unique reason for changing (kx,ky) as I arguing above.

Finally, in a 3d contact- molecule- 3d contact (kx,ky) can change although the energy is constant.

Then, I am still confused.

Thank you for your interest

2

General Questions and Answers / Re: Transmission Eigenvalues revisited

« on: October 10, 2010, 20:45 »

Hello Anders,

My system has an infinite 3D electrode + molecule (central region) + infinite 3D electrode. Do you mean that in this kind of system (kx,ky) is conserved?

Best regards

3

General Questions and Answers / Re: Transmission Eigenvalues revisited

« on: October 6, 2010, 21:14 »

Thank you for your quick reply.

I think I have understood the process that takes place if we have a sandwich-like system with the characteristics you describe. However, I think the key of my question could be in the 3D character of the contacts. In those systems, for a fixed energy E0, it is possible to have lots of k-states in the left contact. When we speak about 'transmission' we can speak of several different, but related, issues:

Transmission spectrum for E0: The whole transmission for that energy, taken into account the contribution of all the left k-states with E0. Of course, to calculate the transmission of each of those left k-states we must consider the hamiltonian of the system.

Transmission eigenchannel: A set of left k-states that when travelling through the central zone of the system produce a wavefunction in the right electrode that only have components belonging to the same set of k-states.

T(E,k): (Atomistix toolkit): I think (suppose) it is the k-state components of the wavefunction in the right electrode if we have a pure k-state in the left electrode.

If all the above is true. My question is: ¿is there a relation between T(E,k) and the transmission eigenchannel as I unsderstand them?

Thank you again

I will read carefully the references you sent. My ideas about eigenchannel transmission have been taken from Physical Review B, 76, 115117 (2007)

4

General Questions and Answers / Transmission Eigenvalues revisited

« on: October 6, 2010, 11:59 »

Hello

I know there are several posts about transmission eigenvalues. Particularly good explained is http://quantumwise.com/forum/index.php?topic=349.0. However I have a basic question and I need some support (replies or bibliography) to understand this issue.

My question is: "As far as I understand the concept of "transmission eigenchannel" it refers to a set of k-states in the left electrode that are mapped to the same set of k-states into the right electrode. The procedure to obtain them should be the following: For a fixed energy, we need to calculate for each k-state in the left contact its composition in k-states in the right contact. Once calculated the above for every k-state in the left contact we obtain 1 (and only 1) transmission matrix, which depends on energy but not in k. The diagonalization of that matrix provides a several sets of k-states.

However, atk calculates the transmission eigenvalues depending on energy and left k-point, T(E,k), and you wrote that for a particular energy E and k-point k, you take the trace of tt^\dag. So my questions are the following : for every E, and every k, do you calculate one transmission matrix? The procedure is not to build one transmission matrix which contains every k-point for a fixed energy and calculate the trace?


If this is correct, which is the relation between 'my' transmission eigenchannel and yours?"

PD: We're considering 3-D contacts.

5

General Questions and Answers / Re: Eigenchannel Transmission

« on: April 27, 2010, 10:17 »

Thank you

6

Future Releases / Re: What is your Linux distribution?

« on: April 25, 2010, 20:02 »

Ubuntu 9.10

7

General Questions and Answers / Eigenchannel Transmission

« on: April 25, 2010, 19:58 »

Hello

I'm sorry if this is a basic question but I have not found the correct answer.

The question is:

'I would like to obtain the transmission of each eigenchannel for a 3D two-probe system.
The way I try it is
  1. I make up a Morhkost grid.
  2. For each energy
     2.1. For each k-point
           2.1. I use the function calculateTransmissionEigenchannel for that energy and k-point. In this way I obtain the transmission for each eigenchannel at that energy and k-point.
     2.2. For each eigenchannel I sum the results of the above k-point loop and divide by NumberOfKpoints*NumberOfKpoints.
The results are right but the program is too slow.

Is there an alternative procedure, as calculateTransmissionSpectrum, but that provides information for each channel?'

Thank you

8

Installation and License Questions / Re: FAQ: libg2c.so.0: cannot open shared object file: No such file or directory

« on: March 8, 2010, 12:42 »

I need to obtain libg2c in Ubuntu 9.10

Any idea about it?

Thank you

9

General Questions and Answers / Re: Disagree of the transmission spectrum and transmission obtained with T(k,E)

« on: January 15, 2010, 15:58 »

Thank you 

10

General Questions and Answers / Re: Disagree of the transmission spectrum and transmission obtained with T(k,E)

« on: January 14, 2010, 13:31 »

Thank you very much for your reply but I am not sure to understand the answer. What do you mean with 'the right way'? In the script calc_transmission_reduced_grid.py provided with the tutorial Tutorial_Transmission_Coefficientes.pdf the transmission spectrum is obtained with the line 'TE = sum(sum(tr_reconstructed))/(N*N)'. Thus, if I calculate in that way the transmission spectrum I think I should have the same results than if it is calculated by the function calculateTransmissionSpectrum, as I posted above. However when I tried it the results were not exactly the same and I want to know if it is because ATK's functions or because I have not understood correctly the procedure.

I will also try with the exact example of the tutorial, I mean with femgofe_antipara.nc.

Thank you again

11

General Questions and Answers / Disagree of the transmission spectrum and transmission obtained with T(k,E)

« on: January 13, 2010, 13:03 »

Hello everybody,

my question is the next one: I think atk provides 2 'equivalent' ways to obtain the transmission spectrum:
  1. Calculate T(E,k) and integrate in k. If the used k's are obtained with the Monhkorst procedure, T(E) is obtained straightforward by adittion and divide by N^2.
  2. Use Trasmission spectrum function.
The question is: Should both approaches provide the same results?

Thus, I have calculated a .nc file with a selfconsistent_calculation, load a variable scf_calc with those data and set up this script by changing few things of that provided by the tutorial 'Transmission Coefficients'

#First way
N=        10
T=        []
K=        []
energies= numpy.arange(-5,5,0.1)*electronVolt
reduced_grid= MonkhorstPackGrid_ReducedToFirstOctant(N)
K=            reduced_grid.getPickedKPoints()
for E in energies:
 tr_limited = calculateTransmissionCoefficients(
  self_consistent_calculation=scf_calc,
  energy = E,
  quantum_numbers = K
 )
 tr_reconstructed = reduced_grid.reconstructT(tr_limited)
 TE = sum(sum(tr_reconstructed))/(N*N)
 if processIsMaster():
  print E,TE
  if -1e-3*eV<E<1e-3*eV:
   saveTransmissionCoefficients(tr_reconstructed,'trcoeff_k100Red_E0eV.cpk')

#Second way
bzip= brillouinZoneIntegrationParameters((N,N))
electron_transmission = calculateTransmissionSpectrum(
 self_consistent_calculation = scf_calc,
 energies = energies,
 brillouin_zone_integration_parameters=bzip
 )
energies = electron_transmission.energies()
coefficients = electron_transmission.coefficients()
if processIsMaster():
   print 'Energy (eV)      Transmission'
   print '-----------------------------------'
   for i in range(len(energies)):
      print "%g\t%g" % ( energies.inUnitsOf(eV),coefficients )



Thank you

12

Installation and License Questions / Installing atk-2008.10.0 for 64 bits instead of 32 bits

« on: August 19, 2009, 13:49 »

Hi,

I've got a Intel Core 2 Quad CPU with Ubuntu 8.04 and kernel 2.6.24-24 generic.

If I install atk-2008.10.0 for i386 I have no problem for running but with atk-2008.10.0 for x64 and write

atk --version

or

atk -version

the machine answers with the next message:

/usr/local/atk-2008.10.0/bin/atk_exec:  3: Syntax error: Unterminated quoted string

Can you help me to make the 64 bits version to work?

Thanks

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