Author Topic: Is it able to perform CDFT calculation  (Read 250 times)

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Offline NosCC

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Is it able to perform CDFT calculation
« on: March 1, 2021, 17:47 »
I would like to calculate the excited-state properties e.g. zero phonon line, photoluminescence spectrum etc. What I found is that I have to perform constrained-occupation DFT (CDFT) method, so how can I perform CDFT method in QuantumATK?

Offline mlee

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Re: Is it able to perform CDFT calculation
« Reply #1 on: March 1, 2021, 19:53 »
Unfortunately, QuantumATK doesn't have the CDFT feature.

Offline NosCC

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Re: Is it able to perform CDFT calculation
« Reply #2 on: March 11, 2021, 06:30 »
Thank you for your reply. But what if I apply delta scf method which seems available in ground-state softwares i.e. VASP, QE etc. Is QuantumATK also be able to run that method?
« Last Edit: March 11, 2021, 06:38 by NosCC »

Offline Anders Blom

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Re: Is it able to perform CDFT calculation
« Reply #3 on: March 16, 2021, 19:17 »
I am not too familiar with how this works in other codes, but if you are interested in e.g. charged point defects, QuantumATK has a really broad and powerful set of features for this, see https://docs.quantumatk.com/tutorials/charged_point_defect_study_object

Offline NosCC

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Re: Is it able to perform CDFT calculation
« Reply #4 on: March 18, 2021, 07:40 »
Thank you for your suggestion. However, what I am referring to is not the charge defect calculation. Basically, I believe charge-point defects result from adding/removing some electrons to the structure.  I knew this feature QuantumATK works very well. But I would like to manually occupy the kohn-sham levels. For example, I would like to excite an electron from band#100 to band#101 (assume the ground state is a closed shell singlet). How can I implement it?

Offline Anders Blom

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Re: Is it able to perform CDFT calculation
« Reply #5 on: March 18, 2021, 09:02 »
As far as I can see that is not possible in QuantumATK. I am still not sure it's possible in VASP but it does seem to be included in Abinit (https://forum.abinit.org/viewtopic.php?f=8&t=5186) and there are some interesting applications done with GPAW (https://backend.orbit.dtu.dk/ws/portalfiles/portal/4819779/Mads.pdf).

A quick check on the internet for "delta scf vasp" brought up this page
https://www.vasp.at/forum/viewtopic.php?t=17172
which seems to indicate the same as my point above (but, the page is 5 years old) and links further to
https://www.vasp.at/forum/viewtopic.php?t=17117
which mainly discusses charged defects, hence my previous comment.

However, I don't think the kind of "Delta SCF" they discuss there is the same as in the papers by Voorhis et al, so it's a bit misleading.

I am quite curious what the purpose of exciting individual electrons is? If it's something that could benefit a lot of users, we might consider implementing it, or perhaps something like XDFT (https://arxiv.org/pdf/1803.01421.pdf).
« Last Edit: March 18, 2021, 09:08 by Anders Blom »

Offline NosCC

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Re: Is it able to perform CDFT calculation
« Reply #6 on: March 18, 2021, 09:33 »
Your links from both Abinit and GPAW are what we are discussing whereas the VASP's link is not. What I am quite sure to employ delta scf via VASP is based on this
 https://wiki.kfki.hu/nano/Easy_manual_occupancy_of_Kohn-Sham_levels_with_FERWE_and_FERDO
and
https://www.vasp.at/forum/viewtopic.php?f=4&t=358

For its advantages, I would say that I do not know much but at least I believe we can calculate some excited-state properties without involving in time-dependent DFT like in excited-state DFT codes (Gaussian etc), so implementing XDFT would be great.