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Topics - hagelberg

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I'd like to compute spin projections of the Hartree Difference Potential, specifically projections on spin-up/spin-down populations, and the difference between both. Could you suggest a script that would achieve this? I have access to QuantumATK S-2021.06. Thanks!

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General Questions and Answers / Rashba effect
« on: July 16, 2020, 18:55 »
Hello - I have a question  about the extent to which the Rashba effect can be included in transport computations with ATK (version 2018.6 or higher).  While there are various versions of the Rashba effect, I want to understand this effect broadly as the interaction of an electron spin with an electric field applied in a direction perpendicular to the electron momentum. To a degree, such an interaction is certainly represented in ATK.  If we  expose a device to a perpendicular electric field and allow for non-collinear spins, we'll calculate the impact of the electrically modified device on the spins of the electrons traversing the device.  I'd like to find out if ATK includes, in addition, the interaction between the electron spins and the screened perpendicular electric field (which one might describe by a Hamiltonian of the form H_R ~ -\sigma . (p X E/2 m), with sigma as the array of spin matrices, p as the electron momentum, and E as the electric field).

Thanks,
Frank

3
Hello,

I struggle with memory restrictions when running device jobs. Two questions in this context:

(1) When trying to run a spin-orbit calculation involving a device (SOGGA, OMX - please see attached .py file), I came in conflict with machine memory caps. I consulted online advice on how to reduce the memory demands of my job (e.g.  https://docs.quantumatk.com/technicalnotes/advanced_performance/advanced_performance.html) and implemented what I found (see the Device Algorithm Settings block in the attached .py file). In this case, I received an error message that I couldn't decipher:

"Calculating Density Matrix :
** Back Engine Exception : info is nonzero
** Location of Exception : greensfunctioncalculator.cpp:843"
(see the attached output file)

This probably has to do with some erroneous algorithm settings. Could you give me some advice on this?

(2) Is there some way to determine the overall memory required by an ATK job? This would be extremely helpful. It happens very often that I start a job successfully, just to find it terminated with a memory error after many hours of running time.

Thanks,
Frank Hagelberg

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Dear Sir/Madam

Here's my problem: whenever I load any file into Builder, VNL crashes.
This does not happen when I use the Builder Plugin option. In this case, the chosen structure appears in the Builder window, and I can manipulate it using the Builder tools. However, when I try to load a second structure from the Plugin menu into the Builder, I get an error message (attached: Error1).
Also, trying to close Builder yields an error message (attached: Error2).

I'm using QuantumATK 2018.06. The operating system of my computer is Windows 7 Enterprise.
I installed QuantumATK 2018.06 one year ago and until now did not encounter any problems related to Builder. I checked if some destructive interference with recent computer updates could be at the root of the sudden trouble. This does not seem to be the case.

I realize that there is some material on VNL crashes due to Builder on this forum, but I did not find anything that obviously speaks to the problem at hand.

Thanks,
Frank

5
Hello,
I have a question related to QuantumATK-2018. Enclosed is an input file (aGNR-2Fe….) for a device calculation involving an armchair graphene nanoribbon (aGNR) with substitutional Fe atoms. This is part of a follow-up project of an earlier study on the spin-filtering efficiency of aGNRs with embedded transition metal impurities (F. Hagelberg, A.Kaiser, I.Sukuba, M. Probst, Mol. Phys. 115, 2231 (2017)). The earlier work was done with ATK-2015. Trying to reproduce some of the previous results with QuantumATK-2018, I fail completely. The atomic populations seem to oscillate between a physically reasonable state and an unphysical state that includes extremely high atomic populations at the ends of the central region. I enclose the output file corresponding (atkjob-aGNR-2Fe…I reduced the size a bit) for illustration (see, for instance, the last population block in that file). I tried to attain convergence by varying the DFT methd (i.e. GGA versus LDA, DFT+U) as well as the exchange-correlation functional, but this didn’t improve the erroneous output. Are there some critical DFT-related features in QuantumATK-2018 that were not present in ATK-2015, and that I possibly mishandle?

Thanks,
Frank Hagelberg

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