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### Messages - bubble

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1
##### General Questions and Answers / Re: questions about surface green's function(SGF)
« on: March 24, 2024, 05:46 »
Any suggestion?thank you！

2
« on: February 26, 2024, 08:53 »
Hi,  I intend to invesigate a system (i.e.  a 2D material on the metal substrate) using SGF. The version of QATK used here is the newest, and for this system the metal substrate is set to half-infinite according to SGF (in other words, I intend to place the 2D material  on one surface of the metal substrate, while the other "surface" of the metal substrate being set to has the periodic boundry condition).

Now I have several questions about SGF.

1. SGF method can be used to this "2D material + metal substrate" system?

2.  SGF method can be used to optimize the structure of this system ?

3. SGF method can be used to calculate the electronic structure of this system? (e.g. energy band, DOS etal.)

4. The charge transfer between the 2D material and the metal substrate can be calculated using SGF?

3
##### General Questions and Answers / Re: Boundary Condition at finite bias
« on: December 18, 2017, 15:26 »

https://docs.quantumwise.com/manuals/technicalnotes/hartree_potential/hartree_potential.html

Thank you.
I obtain the explanation of Dirichlet condiction from the ATK maunual (see the above link). So minor correction may be neccesary to avoid more misunderstanding.

4
##### General Questions and Answers / Boundary Condition at finite bias
« on: December 18, 2017, 15:13 »
For a device simulation, when it is under the finite bias, I found the  default boundary  condition for the C direction (Left, Right) are both Dirichlet condition. To my knowledge, this condition means that 'The Hartree potential is zero at the boundary'. However, because the device is under finite bias voltage (that is, the chemical potential, or electropotential is different). Then, it seems that the Dirichlet condition can not apply to left-electrode-center-region interface and right-electrode-center-region at the same time ?  Should I change the default Dirichlet condition to other condition such as  Neumann?

Thank you.

5
##### General Questions and Answers / Re: can one adjust Fermi level by setting the electrodes have same voltages?
« on: December 18, 2017, 07:43 »

6
##### General Questions and Answers / Re: can one adjust Fermi level by setting the electrodes have same voltages?
« on: December 13, 2017, 12:54 »

I calculated an example, i.e. the Fe-MgO-Fe MTJ in the database. I set the VL=VR=0 or VL=VR=0.5 V for the device (see the attachment for the two input py files, here SE method is employed, version=ATK2017.2). But I found the spectra are very different (see the third attachment file). How to explain this?

7
##### General Questions and Answers / Re: can one adjust Fermi level by setting the electrodes have same voltages?
« on: December 8, 2017, 12:11 »
Sometimes we need to change the Fermi level of  a system. Of course, there are many different methods for this. For example, by changing gate voltages or by doping atoms etc.

Now, my question is, for the device configuration in ATK, whether I can apply the SAME voltages to the left and right electrodes to shift the Fermi level of the device?  For example, if I set VL=VR=0.5 V (VL, VR are the voltages of the two electrodes). Then,  in present case,  the device is still in equilibrium (there is NO current). After SCF loops, I will obtain many transport properties. e.g. transmission spectra.  I want to know whether the obtained spectra are the result  after the Fermi level is shifted by 0.5 eV?

8
##### General Questions and Answers / can one adjust Fermi level by setting the electrodes have same voltages?
« on: December 7, 2017, 10:45 »
Hi,
Now I have a question. If I want to adjust the Fermi level of a device. For example, if I set VL=VR=0 V, then I can obtain the transmission spectrum at zero bias. However, If I set VL=VR=0.5 V, can I obtain the transmission spectrum (at equilibrium) corresponds to the whole Fermi level is shifted by 0.5 eV?

Thank you.

9
##### General Questions and Answers / Re: A strange phenomenon in ATK
« on: November 11, 2017, 08:58 »
Could you post the python script and log file related to this calculation?

Unfortunaly, I delete the original py, hdf5 and log files. However, If I have meet this problem again, I will send the results to your support email.

10
« on: November 11, 2017, 08:56 »
Yes, it is correct. I also notice that Si is doped with electrons, so that there exist additional carriers in the conduction band (i.e., for energies > e_R) to contribute to the current, compared to intrinsic Si.

Thank you for your reply. Although I still feel the discussion is a little against my intuition. it seems that there is no better explanation for this so far.  Thank you!

11
« on: November 10, 2017, 12:01 »
The calculation of the current is done at a finite temperature, meaning that there are electrons populating the conduction band states in the electrodes.
Hi, Petr, I upload the figure. You mean that the states indicated by the red arrows are used to deliver the electrons?

12
« on: November 10, 2017, 08:42 »
https://docs.quantumwise.com/tutorials/nisi2-si/nisi2-si.html

In the above tutorial, the last but one figure gives the PLDOS of a 'forward-bias' PLDOS (Vb=0.3V). One can see that in the bias window (energy bewteen eL and eR), there are no states in the right electrode (corresponding the area in the energy range eL-eR is black if z is larger than. e.g. 60 A).   However, the tutorial discussed that ' here the electrons do not have to overcome any potential barrier, so that the current will be higher. '

I want to know what states are used to carry these electrons? Since in the bias window, for the right electrode, it seems that there donot exist any states!

Thank you!

13
##### General Questions and Answers / A strange phenomenon in ATK
« on: November 10, 2017, 04:22 »
Hi,
Recently, I used ATK 2017 to calculate the I-V curve in a molecular magnetic tunneling junction (MTJ) at its antiparallel (AP) spin configuration (i.e. the spins on two electrodes are opposite).  I found a very strange phenomenon. i.e. the I-V curve is not symmetrical at high negative and positive bias voltages (+-0.5 V). Please note that the geometric structure of MTJ is symmetrical (i.e., there is a mirror symmetry pendicular to z axis, only the spins on two electrodes are opposite ).
Then, I carefully read some references, and found that this phenomenon is not unique.  For example, see DOI: 10.1039/c4ra09279a (Figure 3b), or DOI: 10.7498/aps.66.198503 (Figure 2b). Please note that although the second example is not written in English, it is not hard to understand the meaning of the figure. In the two examples, the geometric structures is symmetrical (this can also be verified from the LDOS, various eigenstates etc.) , but at high bias voltage, the spin current is asymmetrical.

At AP configuration, if the device is symmetrical (have mirror symmetry), one spin in one electrode should be identical to another spin in another electrode. According to symmetry, at +-Vb, the spin currents should be 'identical', except a sign indicating the direction. This should be indenpent on the details of the device. So, is there anything wrong in the calculation?

14
##### General Questions and Answers / Re: What dose DD mean in the log file
« on: October 31, 2017, 05:10 »
Thank you the quantum staffs for replying my question.

However, I have three quesitons
1. I still don't understand why the DM for an atom is only a number rather than matrix. Because I think the dimension of the DM should depend on, e.g., the basis sets etc. am i wrong? (Below is three adjacent SCI-loops in a log file. )
2. How to obtain DD?
3. For a nonmagnetic system, if its total electron number is odd, shoud spin-polarized calculation be included in ATK? (like some other plane-wave-based codes do)

+------------------------------------------------------------------------------+
| Density Matrix Report                      DM     DM[D]      DD           |
+------------------------------------------------------------------------------+
|   0  Cu   [  0.000 ,  0.000 ,  0.000 ]    5.77870   5.54062   0.31932        |
|   1  Cu   [  1.278 ,  0.000 , -2.068 ]    5.68480   5.28859  -0.02661        |
|   2  Cu   [  0.000 ,  2.068 , -1.278 ]    5.68480   5.28859  -0.02661        |
|   3  Cu   [  2.068 ,  1.278 ,  0.000 ]    5.68480   5.28859  -0.02661        |
|   4  Cu   [  2.068 , -1.278 ,  0.000 ]    5.68480   5.28859  -0.02661        |
|   5  Cu   [  0.000 , -2.068 , -1.278 ]    5.68480   5.28859  -0.02661        |
|   6  Cu   [ -1.278 ,  0.000 , -2.068 ]    5.68480   5.28859  -0.02661        |
|   7  Cu   [ -2.068 ,  1.278 ,  0.000 ]    5.68480   5.28859  -0.02661        |
|   8  Cu   [  0.000 ,  2.068 ,  1.278 ]    5.68480   5.28859  -0.02661        |
|   9  Cu   [  1.278 ,  0.000 ,  2.068 ]    5.68480   5.28859  -0.02661        |
|  10  Cu   [  0.000 , -2.068 ,  1.278 ]    5.68480   5.28859  -0.02661        |
|  11  Cu   [ -2.068 , -1.278 ,  0.000 ]    5.68480   5.28859  -0.02661        |
|  12  Cu   [ -1.278 ,  0.000 ,  2.068 ]    5.68480   5.28859  -0.02661        |
+------------------------------------------------------------------------------+
|   1 E = -25.4904 dE =  2.719759e+00 dH =  2.467539e-01                       |
+------------------------------------------------------------------------------+

|--------------------------------------------------|
Calculating Eigenvalues    : ==================================================
Calculating Density Matrix : ==================================================

+------------------------------------------------------------------------------+
| Density Matrix Report                      DM     DM[D]      DD           |
+------------------------------------------------------------------------------+
|   0  Cu   [  0.000 ,  0.000 ,  0.000 ]    5.66884   5.36145   0.03028        |
|   1  Cu   [  1.278 ,  0.000 , -2.068 ]    5.69131   5.30617  -0.00252        |
|   2  Cu   [  0.000 ,  2.068 , -1.278 ]    5.69131   5.30617  -0.00252        |
|   3  Cu   [  2.068 ,  1.278 ,  0.000 ]    5.69131   5.30617  -0.00252        |
|   4  Cu   [  2.068 , -1.278 ,  0.000 ]    5.69131   5.30617  -0.00252        |
|   5  Cu   [  0.000 , -2.068 , -1.278 ]    5.69131   5.30617  -0.00252        |
|   6  Cu   [ -1.278 ,  0.000 , -2.068 ]    5.69131   5.30617  -0.00252        |
|   7  Cu   [ -2.068 ,  1.278 ,  0.000 ]    5.69131   5.30617  -0.00252        |
|   8  Cu   [  0.000 ,  2.068 ,  1.278 ]    5.69131   5.30617  -0.00252        |
|   9  Cu   [  1.278 ,  0.000 ,  2.068 ]    5.69131   5.30617  -0.00252        |
|  10  Cu   [  0.000 , -2.068 ,  1.278 ]    5.69131   5.30617  -0.00252        |
|  11  Cu   [ -2.068 , -1.278 ,  0.000 ]    5.69131   5.30617  -0.00252        |
|  12  Cu   [ -1.278 ,  0.000 ,  2.068 ]    5.69131   5.30617  -0.00252        |
+------------------------------------------------------------------------------+
|   2 E = -28.2305 dE =  2.740125e+00 dH =  1.336710e-01                       |
+------------------------------------------------------------------------------+

|--------------------------------------------------|
Calculating Eigenvalues    : ==================================================
Calculating Density Matrix : ==================================================

+------------------------------------------------------------------------------+
| Density Matrix Report                      DM     DM[D]      DD           |
+------------------------------------------------------------------------------+
|   0  Cu   [  0.000 ,  0.000 ,  0.000 ]    5.59103   5.26557  -0.14340        |
|   1  Cu   [  1.278 ,  0.000 , -2.068 ]    5.69673   5.31522   0.01195        |
|   2  Cu   [  0.000 ,  2.068 , -1.278 ]    5.69673   5.31522   0.01195        |
|   3  Cu   [  2.068 ,  1.278 ,  0.000 ]    5.69673   5.31522   0.01195        |
|   4  Cu   [  2.068 , -1.278 ,  0.000 ]    5.69673   5.31522   0.01195        |
|   5  Cu   [  0.000 , -2.068 , -1.278 ]    5.69673   5.31522   0.01195        |
|   6  Cu   [ -1.278 ,  0.000 , -2.068 ]    5.69673   5.31522   0.01195        |
|   7  Cu   [ -2.068 ,  1.278 ,  0.000 ]    5.69673   5.31522   0.01195        |
|   8  Cu   [  0.000 ,  2.068 ,  1.278 ]    5.69673   5.31522   0.01195        |
|   9  Cu   [  1.278 ,  0.000 ,  2.068 ]    5.69673   5.31522   0.01195        |
|  10  Cu   [  0.000 , -2.068 ,  1.278 ]    5.69673   5.31522   0.01195        |
|  11  Cu   [ -2.068 , -1.278 ,  0.000 ]    5.69673   5.31522   0.01195        |
|  12  Cu   [ -1.278 ,  0.000 ,  2.068 ]    5.69673   5.31522   0.01195        |
+------------------------------------------------------------------------------+
|   3 E = -30.0083 dE =  1.777799e+00 dH =  8.903270e-02                       |
+------------------------------------------------------------------------------+

15
##### General Questions and Answers / Re: Is it a bug?
« on: October 27, 2017, 13:16 »
@bubble Thanks a lot for your report. I will create an internal bug report on this. It would also be helpful to have your output nc-files  and full log file. I guess the files are quite bulky. So, could you then put it in Dropbox and send us a link? You may send the links through our support channel, support@quantumwise.com, if you do not feel like sharing the links publicly.
The link to the py and log files has been sent to the 'support' email.

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