Is this EDP curve correct?

[lknife]

Hello,

I made a device configuration and calculated the EDP curve of it. However, there is something I cannot understand. Please see the attached figure of the EDP plot and the .py file for it, notifying the Y value of the plot. Can anybody here tell me if the EDP curve is correct? I used the ATK 2016.4 to do the calculation.

Thank you very much for your help!

[Petr Khomyakov]

It might be that you have chosen Sum instead of Average for Projection type while plotting the potential in the 1D Projector. This could in principle give you such huge numbers for the potential.

[lknife]

Thank you very much for your reply.
However, I do chose the "average" for the Projection type. If I choose the type to "Sum", the figure will be shown as the attached file.

[Jess Wellendorff]

Looks like your NEGF calculation did not converge. Check the ATK log file.

[Daniele Stradi]

Could you please have a look at the density matrix of the last SCF loop in your output file? In particular, the two columns DM (density matrix) and DD (density difference).

+------------------------------------------------------------------------------+
| Density Matrix Report                       DM        DD                     |
+------------------------------------------------------------------------------+
|   0  In   [ -0.000 ,  0.000 ,  0.000 ]    3.52719   0.52719                  |
|   1  As   [  1.520 ,  1.520 ,  1.520 ]    4.47281  -0.52719                  |
+------------------------------------------------------------------------------+
|   3 E = -2.67569 dE =  2.502366e-04 dH =  9.448242e-05                       |
+------------------------------------------------------------------------------+

My first guess is that the charge density has been drained away from the central region due to inappropriate simulation parameters. In this case, the column DM should be 0.0.
Regards,
Daniele

[lknife]

Looks like your NEGF calculation did not converge. Check the ATK log file.

You are right: I have checked the .log file and the calculation did not converge. Another question: how to make it converge? What parameters should I tune, or I need to modify my device configuration?

Thank you very much for your kind help!

[lknife]

+------------------------------------------------------------------------------+
| Density Matrix Report                       DM        DD                     |
+------------------------------------------------------------------------------+
|   0  In   [ -0.000 ,  0.000 ,  0.000 ]    3.52719   0.52719                  |
|   1  As   [  1.520 ,  1.520 ,  1.520 ]    4.47281  -0.52719                  |
+------------------------------------------------------------------------------+
|   3 E = -2.67569 dE =  2.502366e-04 dH =  9.448242e-05                       |
+------------------------------------------------------------------------------+

...In this case, the column DM should be 0.0.

Thank you very much for you help! I have a question about the words marked in blue: if DM=0.0, is it correct or incorrect?

[Jess Wellendorff]

DM means DensityMatrix, so if DM=0.0 there are no valence electrons  on that atomic site, which is almost always very bad and indicates poor SCF convergence. You need to inspect the SCF convergence in order to figure out how to fix it. Perhaps it will converge in 20 more iterations? Perhaps electrons are depleted from the central region - electrode boundaries, in which case you perhaps need to use longer electrodes, etc. It's impossible to give a completely general recipe for this kind of thing.

[lknife]

Thank you very much for your explanation!

The followings are part of the .log file about the SCF iteration (the full file is too big to be posted here). Could you please have a loot at it to see what's wrong with it?

Thanks a lot again for your kind help!

------------------------------------------------------------

     |--------------------------------------------------|
Calculating Density Matrix : ==================================================
+------------------------------------------------------------------------------+
| Density Matrix Report                         DM     DM[D]      DD        |
+------------------------------------------------------------------------------+
|   0  Te   [  16.799 ,   0.875 ,   0.801 ]    7.29316   7.29194  -1.41489     |
|   1  Te   [  13.695 ,   2.624 ,   1.739 ]    0.11796   0.11840 -15.76363     |
|   2   W   [  15.353 ,   0.875 ,   3.303 ]    6.29553   6.29539  -1.40908     |
|   3  Te   [  17.473 ,   2.624 ,   3.891 ]   -0.09463  -0.09465 -16.18927     |
|   4  Te   [  13.022 ,   0.875 ,   4.836 ]    6.81351   6.81183  -2.37466     |
|   5   W   [  15.142 ,   2.624 ,   5.509 ]    5.36223   5.36642  -3.27135     |
|   6  Te   [  16.799 ,   0.875 ,   7.111 ]    4.26804   4.26763  -7.46433     |
|   7  Te   [  13.695 ,   2.624 ,   8.048 ]    4.52539   4.52769  -6.94692     |
|   8   W   [  15.353 ,   0.875 ,   9.612 ]    9.01083   9.01866   4.02949     |
... ...
|  83   W   [  14.628 ,   2.624 ,  88.339 ]    4.99012   5.02517  -3.98470     |
+------------------------------------------------------------------------------+
| 498 E =  -747.46 dE =  5.595637e+01 dH =  2.538735e+02                       |
+------------------------------------------------------------------------------+

                            |--------------------------------------------------|
Calculating Density Matrix : ==================================================
+------------------------------------------------------------------------------+
| Density Matrix Report                         DM     DM[D]      DD        |
+------------------------------------------------------------------------------+
|   0  Te   [  16.799 ,   0.875 ,   0.801 ]    6.79753   6.84718  -2.35530     |
|   1  Te   [  13.695 ,   2.624 ,   1.739 ]    0.17277   0.17969 -15.64754     |
|   2   W   [  15.353 ,   0.875 ,   3.303 ]    6.41454   6.41024  -1.17522     |
|   3  Te   [  17.473 ,   2.624 ,   3.891 ]   -0.09635  -0.09908 -16.19542     |
|   4  Te   [  13.022 ,   0.875 ,   4.836 ]    6.15977   6.15823  -3.68200     |
|   5   W   [  15.142 ,   2.624 ,   5.509 ]    5.34169   5.33755  -3.32076     |
|   6  Te   [  16.799 ,   0.875 ,   7.111 ]    5.57543   5.56182  -4.86275     |
|   7  Te   [  13.695 ,   2.624 ,   8.048 ]    4.90536   4.89295  -6.20169     |
|   8   W   [  15.353 ,   0.875 ,   9.612 ]    9.02604   9.02771   4.05374     |
... ...
|  83   W   [  14.628 ,   2.624 ,  88.339 ]    2.57530   2.48627  -8.93844     |
+------------------------------------------------------------------------------+
| 499 E = -667.988 dE =  7.947253e+01 dH =  2.527983e+02                       |
+------------------------------------------------------------------------------+
################################################################################
#                                                                              #
# Warning: The calculation did not converge to the requested tolerance!        #
#                                                                              #
################################################################################

[Anders Blom]

What version of ATK is this?

[Jess Wellendorff]

Perhaps you can also attach the ATK script?

[lknife]

I am using ATK2016.4.

After increasing the k-point sampling from (1 7 50) to (1 9 100) and tuning some parameters such as dampling factor (from 0.1 to 0.3) and history step (from 20 to 12), the EDP curve is now converged. I think the insufficient k-point sampling may be the main reason to the problem.

Thanks a lot to all of you!

[Anders Blom]

Esp. in the C direction. It's typically not sufficient to use 50 points, unless you have a very long electrode in the first place.