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Topics - mephisto3142001

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1
General Questions and Answers / The relation between Transmission Spectrum and Density of state
« on: May 21, 2012, 02:44 »
The plot of Transmission Spectrum is always similar to that of Density of state, and I have consulted the derivation of Transmission Spectrum
from papers and textbooks, showing that calculating Density of state is a required step in the beginning. I want to ask the exact meaning of
Transmission Spectrum and how it is correlated to Density of state.

2
General Questions and Answers / Transmission eigenstate and scattering state
« on: March 26, 2012, 12:09 »
Hello
I have some questions about Transmission eigenstate.
1. Does Transmission eigenstate mean electron scattering state in central region of devices?
2. If the isosurface of Transmission eigenstate at a particular energy point resembles MPSH of quantum number N,
   whether the transmission coefficient at the same energy point is mostly contributed from MPSH of quantum number N?

3
General Questions and Answers / number of electrons report
« on: March 13, 2012, 19:51 »
I calculated the Molecular Energy Spectrum of DTB and saw number of electrons report . I thought that the number of valence electrons is 40(6x4(Carbon)+1x4(Hydrogen)+6x2(Sulfur)=40). Furthermore, there is a statement "An isolate DTB molecule has 40 valence electrons" in paper, Comp. Mat. Sci., 27, 151, 2003.
However, the result I got showed  Number of electrons = 42.000000. Please help me solve this problem.

+------------------------------------------------------------------------------+
| Molecular Energy Spectrum Report                                             |
| ---------------------------------------------------------------------------- |
| Fermi level = -2.452011e+00                                                  |
| Number of electrons = 42.000000                                              |
| Unit = eV                                                                    |
| Eigenenergies given relative to the Fermi Level                              |
+------------------------------------------------------------------------------+

    0  -1.762873e+01   2.000000e+00
    1  -1.610272e+01   2.000000e+00
    2  -1.459204e+01   2.000000e+00
    3  -1.450402e+01   2.000000e+00
    4  -1.276223e+01   2.000000e+00
    5  -1.121167e+01   2.000000e+00
    6  -1.042559e+01   2.000000e+00
    7  -8.782769e+00   2.000000e+00
    8  -7.705019e+00   2.000000e+00
    9  -7.369467e+00   2.000000e+00
   10  -6.677567e+00   2.000000e+00
   11  -6.438039e+00   2.000000e+00
   12  -5.800967e+00   2.000000e+00
   13  -5.079045e+00   2.000000e+00
   14  -4.709258e+00   2.000000e+00
   15  -4.549146e+00   2.000000e+00
   16  -3.290120e+00   2.000000e+00
   17  -3.281403e+00   2.000000e+00
   18  -3.142225e+00   2.000000e+00
   19  -2.588342e+00   2.000000e+00
   20  -1.804314e+00   2.000000e+00
   21   2.410416e+00   6.424856e-41

4
General Questions and Answers / Question about k-point Sampling and Monkhorst Pack Grid method
« on: March 13, 2012, 15:56 »
Greetings, I have three questions concerning k-points sampling.

1.As we set parameters for "k-point Sampling", we type three integers "(nA, nB, nC)". If I typed (3, 3, 50), whether it means that I want   
  the whole Brillouin zone to be sampled by 3x3x50=450 k-points? 

2.Does Monkhorst-Pack-Grid method calculate reciprocal lattice vector of each k-point in the whole Brillouin zone via the formula used in "
  Phys. Rev. B., 13, 5188, 1976" ? If I typed (3, 3, 50), can I say that I have Monkhorst-Pack-Grid method generate reciprocal lattice 
  vectors for 450 points?

3.When I calculate TransmissionSpectrum, why can k-points along the C-reciprocal direction be ignored?

5
General Questions and Answers / Questioning the I-V characteristics of DTB device
« on: March 11, 2012, 17:38 »
I compared the result of I-V characteristic of DTB device in tutorial "ATK Tutorial for Molecular Devices"  with the I-V  characteristic published in "Comp. Mat. Sci. 27, 151 (2003) ". The result shows slight difference at the region (1.6V ~ 3.0V and -1.6V ~ -3.0V).          The I-V curve is ohmic with smaller slope in  in tutorial "ATK Tutorial for Molecular Devices". However, the I-V is almost horizontal in "Comp. Mat. Sci. 27, 151 (2003) ". The parameters setting is followed  by both the tutorial and the paper. I deemed that the same calculation method (no matter what package, like TranSiesta or Virtual NanoLab is used) should result in the identical I-V characteristic, so I wonder which one is more correct or which fact may cause such the difference.

6
General Questions and Answers / Calculating transmission spectrum of dithiol benzene (DTB) device with gate elec
« on: February 29, 2012, 13:21 »
I constructed a dithiol benzene (DTB) device instructed from the tutorial "Calculate and analyze a molecular device configuration". After that, I added dielectric region(4ε0) and metallic region(-1 volt) as gate electrode using Builder and then I calculated TransmissionSpectrum (gate voltage was set to be 0 volt). The result was quite weird and very different from the original DTB device without gate electrode. I want to know what the problem it is and find a proper way to solve it. I posted python code and result figure.


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