Messages

1

General Questions and Answers / Re: The relation between Transmission Spectrum and Density of state

« on: May 24, 2012, 07:43 »

I looked up the topic about transmission spectrum somewhere else in the forum and I found a reply "The transmission spectrum is not the probability of an electron going through the device. The transmission spectrum is the sum of probabilities for all the states that exist at the given energy."
I want to confirm whether my concept is correct.
For  transmission spectrum of DTB device, the energy 2.03eV corresponds to transmission coefficient 0.608, does it mean that
the state at 2.03eV has probabilities 0.608 to exist?

2

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.

3

General Questions and Answers / Re: Transmission eigenstate and scattering state

« on: March 27, 2012, 10:57 »

Thanks! I have clarified some conceptions.
According to your answer, the energy level of HOMO doesn't necessarily correspond to the transmission peak near Fermi-level, does it?
it's what I want to make clear.

4

General Questions and Answers / Re: Transmission eigenstate and scattering state

« on: March 27, 2012, 09:29 »

According to the statement above, geometry optimization doesn't affect the value of MolecularEnergySpectrum, does it?

State 21(HOMO) is -1.35eV and it corresponds to the transmission peak near Fermi-level in the paper I quote.
However, my calculated HOMO energy level is -1.80eV, which doesn't correspond to the peak near Fermi-level, that's why
I doubted my result. I want to confirm that whether the energy level of HOMO must correspond to the transmission peak near Fermi-level?

5

General Questions and Answers / Re: Transmission eigenstate and scattering state

« on: March 27, 2012, 07:25 »

Thanks
I calculated TransmissionSpectrum of di-thiol-Benzene device, and the peak near Fermi-level(average Fermi-level) is
at -1.35ev. I also calculated MolecularEnergySpectrum, and the energy level of HOMO is at -1.84eV. I consulted
"Comp. Mat. Sci., 27, 151, 2003" and lots of papers, I found that the energy level of HOMO always corresponds to the
 peak near Fermi-level. The energy level of HOMO is indeed -1.35eV in "Comp. Mat. Sci., 27, 151, 2003". However, my
result showed that the peak is located at region between HOMO and LUMO, which seems unreasonable.
I guessed my problem is due to geometry optimization, but it's just an estimation. I need some advice to solve it.

+------------------------------------------------------------------------------+
| Molecular Energy Spectrum Report                                             |
| ---------------------------------------------------------------------------- |
| Fermi level = -2.451996e+00                                                  |
| Number of electrons = 42.000000                                              |
| Unit = eV                                                                    |
| Eigenenergies given relative to the Fermi Level                              |
+------------------------------------------------------------------------------+
   17  -3.280691e+00   2.000000e+00
   18  -3.141465e+00   2.000000e+00
   19  -2.590715e+00   2.000000e+00
   20  -1.805176e+00   2.000000e+00  HOMO
   21   2.408238e+00   6.989741e-41
   22   2.536180e+00   4.955903e-43

6

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?

7

General Questions and Answers / Re: number of electrons report

« on: March 16, 2012, 09:43 »

here is my script.
please take a look

8

General Questions and Answers / Re: number of electrons report

« on: March 14, 2012, 03:27 »

It was the projection on the DTB molecule.
Why does the projection have two additional electrons than the isolated DTB?

9

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

10

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?

11

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.

12

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.