Messages

1

General Questions and Answers / Parallelization of ProjectedDensityOfStates

« on: July 25, 2024, 06:42 »

Dear users and staffs,
May I know how parallelization works in ProjectedDensityOfStates ? Lets say I have 4 kpoints, does that mean I should use not more than 4 processes in calculation? And how can I know what is the reduced number of kpoints?
Thank you for your attention.

best regars,
sukhito

2

General Questions and Answers / Re: Constraints_data parameter in function "writePOSCAR"

« on: April 15, 2024, 11:48 »

Thanks for your reply.

3

General Questions and Answers / Constraints_data parameter in function "writePOSCAR"

« on: April 10, 2024, 10:43 »

Dear developers and users,
I am using QATK Version: T-2022.03 . May I know how can I pass information to parameter 'constrained_data' within the 'writePOSCAR' function? Thanks for your attention.

best regards
Sukhito Teh

4

General Questions and Answers / Re: Papers related to DFT-PPS method

« on: January 11, 2024, 07:15 »

You can read more about it here: https://docs.quantumatk.com/tutorials/dft_half_pps/dft_half_pps.html. In short, it's an attempt to bring some aspect of empirical pseudopotentials into DFT, but instead of a scissor operator acting on the final band structure (which wouldn't work in Ge for instance) there are shifts being applied within the self-consistent cycle. It does require empirical tuning, i.e. you should know the band gap from experiments to tune the parameters.

We implemented this method quite a long time ago, and honestly have not found much use for it. Since then, we have added DFT+1/2 which seems to be a more robust and general scheme, where the same parameters seem to work for many different systems, although you can fine tune them if you do know the band gap. And of course HSE06 and other hybrid functionals which perform really well in LCAO, and which can be truly predictive of the band gaps of unknown materials.

Thank you, I would look into DFT-1/2; HSE06 is good, I have found good results with them,  the ADMM can even speed up HSE calculation so the efficiency is comparable to regular DFT. However ADMM is not compatible to NEGF, so I am looking for alternatives.

5

General Questions and Answers / Papers related to DFT-PPS method

« on: December 18, 2023, 13:56 »

Dear developers and users,

Do you know any paper that explain how DFT-PPS method works or use the method to correct electronic bandgap? I tried but unable to find any related paper.  Or is there a general guide on how to optimize the parameters?

Thank you for your time.

Best regards,
Sukhito

6

Future Releases / Re: Dielectric Constant with Local Field Effect

« on: December 14, 2023, 12:33 »

Thank you for the reply! I am looking forward to the new feature!

7

General Questions and Answers / Inquiry Regarding Local Dielectric Constant Calculation

« on: December 12, 2023, 04:46 »

Dear developers and users,
I am reaching out to seek assistance in reproducing the results presented in a paper titled "Theory of atomic-scale dielectric permittivity at insulator interfaces" https://journals.aps.org/prb/abstract/10.1103/PhysRevB.71.144104.

I am particularly interested in the calculation of the local dielectric constant. For ionic part, the class 'BornEffectiveCharge' can return values for individual atoms, render the calculation of local dielectric constant feasible. However I can't specify which orbitals to be included in OpticalSpectrum class for calculation of electronic dielectric constant, so I wonder if I can use the derivative functions from Class 'BlochState' to calculate the momentum of individual orbital and thus the local dielectric constant. Could you please provide guidance on whether this approach is viable? Additionally, if there exists a more efficient method for performing the calculations, I would greatly appreciate your insights.

Thank you for your time.

Best regards,
Sukhito Teh

8

Future Releases / Dielectric Constant with Local Field Effect

« on: December 8, 2023, 05:31 »

Dear developers,
From what I understand, the dielectric constant obtained from OpticalSpectrum currently does not account for local field effects, rendering it unsuitable for calculating the dielectric properties of 2D materials. I have observed that QATK now offers GW calculations, and I am curious whether the dielectric tensor involved in GW calculation takes local field effects into consideration. If so, is it possible to save these values for further use?

Thank you for your attention to this matter.

Best Regards,
Sukhito Teh

9

General Questions and Answers / Re: Asking for general guide to speed up geometry optimization

« on: October 27, 2023, 15:23 »

Great.
How many cores you are using & how many atoms?

ranging from 100 to 500 atoms. Using 2-4 process/ 2-4 nodes per k point

10

General Questions and Answers / Re: Asking for general guide to speed up geometry optimization

« on: October 25, 2023, 14:33 »

Welcome
Let me know which one works for you.

Hi, I found out the slow convergence is caused by the ghost atoms . After fixing the coordinates of those ghost atoms (in between VDW layers), the optimization of geometry becomes significantly more efficient.

11

General Questions and Answers / Re: Asking for general guide to speed up geometry optimization

« on: October 22, 2023, 19:00 »

Yes, you are right iteration control affects electronic convergence.

While increasing mesh and K point do help a system converge but it makes it converge slower.
A tip for fast convergence would be:
1. If you are suppose converging an unpolarized system, try first with low k point while keeping mesh cutoff higher or normal is what to be kept. After your system is converged at low K point increase K point to what u want. This can help achieve quicker optimization
2. If you are stuck with polarized optimization, then best is to perform unpolarized optimization first then use converged file to perform polarized optimization. This surely has worked in my case & is well reported method.
3. Another way is to increase your cores or nodes to achieve quicker optimization.
4. If still you are not getting quick optimization, perform a small atomic rattling for your structure in builder and perform any of the above steps. This should help too.
5. If still you are not getting quick optimization, then contact synopsys at solvnet.

Thank you for your useful guide.

12

General Questions and Answers / Re: Asking for general guide to speed up geometry optimization

« on: October 20, 2023, 13:20 »

Try playing with parameters in Iteration control. Look into manual.

Thank you for the suggestion. From what I understand, appropriate iteration control parameter would improve electronic convergence, but having little effect towards ionic (relaxation) convergence. Do you think increase density_mesh_cutoff and kpoints density would help ionic convergence?

13

General Questions and Answers / Asking for general guide to speed up geometry optimization

« on: October 19, 2023, 07:19 »

Dear developers and users,
I am working on optimization of slab system 100 atoms ~ 500 atoms. The SCF convergence is working fine, but the geometry optimization took long time to converge. The total energy of the system did go down slowly with optimization steps, but the force remain in the order of ~ 1eV/A after 100 optimization steps. Is there a general guide to improve the convergence speed of geometry optimization.  Thank you for your attention

Best regards,
Sukhito Teh

14

General Questions and Answers / Re: SurfaceConfiguration not converged properly

« on: October 3, 2023, 10:23 »

Thank you for your reply! I l tried the calculation with more layers of ghost atoms and the result remains similar, anyway I am glad to hear that such results doesn't necessary  means  unreliable calculations. I did check and compare results with different terminations, with/without surface relaxation, as you said, they can indeed make a big difference.

15

General Questions and Answers / SurfaceConfiguration not converged properly

« on: September 30, 2023, 08:11 »

Dear developers and users,
I am trying to calculate work function of TiN using green function method, however the calculation failed to converge nicely at 111 surface, i.e. energy is converged but dQ at central region is still large (~0.15).  The work function obtained seems reasonable, but for other surface calculation, I often obtained dQ that is smaller than 0.01, so I am not sure if I should concern with such value of dQ.

I had also tried different approaches including increases contour points, higher mesh, reducing number of history steps, increase electrode length, central length , but the dQ remained large.

Thank you for your attention