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16 votes
Accepted

Why does Quantum ESPRESSO need 13TB of RAM for a (3x3x3)nm supercell?

Memory use to store the KS orbitals in a plane wave DFT calculation is proportional to cell-volume*number-of-states, and in turn proportional to the square of the number of atoms in the large limit. ...
Keith Refson's user avatar
16 votes

How to understand the spin of exciton?

As you mentioned in the question, excitons are indeed bound electron-hole pairs. They are often considered to be the signature of optical spectra in insulating solids. Adding onto the comment by tmph, ...
Xivi76's user avatar
  • 2,392
11 votes
Accepted

Quantum Dot properties using VASP

Calculation of QD using VASP is not that much different from bulk calculations; you just need to ensure that sufficient vacuum is applied in all 3 spatial dimensions. My experience is that 10-15 ...
liuyun's user avatar
  • 401
9 votes

Why does Quantum ESPRESSO need 13TB of RAM for a (3x3x3)nm supercell?

2000 atoms is quite a lot. If you see 3x3x3, often that's the primitive cell repeated by that much. A 3 nm particle will involve a lot of computational power even with approximations. Be sure you ...
Tristan Maxson's user avatar
9 votes
Accepted

Can deformation potential theory be applied to 2D and 1D systems?

Deformation potential theory is almost always used to study 2D materials. The first line of the abstract of the original Bardeen-Shockley paper mentions "deformations of the crystal lattice"....
Nike Dattani - No Free Time's user avatar
9 votes

How to understand the spin of exciton?

First I mention this very similar question on Physics SE and the related answer. Then, a couple of points which are not well addressed in the previous answer in my opinion. First of all we are here ...
Davide Sangalli's user avatar
9 votes

How can I know if 3D aperiodic systems are not interacting with each other using Quantum ESPRESSO?

Since QE is a planewave based code and we are talking about cells, its important to realize its periodic so its always interacting with itself to some degree. The only way to check if its ...
Tristan Maxson's user avatar
6 votes

Quantum Dot properties using VASP

It is worthwhile to add to liuyun's answer that even though these calculations are in theory straightforward there are some caveats you have to acknowledge. Band gap tends to be underestimated by ...
Tristan Maxson's user avatar
6 votes

Geometrical Optimization not converging for a double perovskite quantum dot, using Gaussian

OK, I do not want to be that guy, but I will be that guy. Some general remarks You should plan better your calculation projects. You got 129 SCF cycle calculated in about 3 days. Even if this ...
Greg's user avatar
  • 1,807
5 votes

Geometrical Optimization not converging, where am I going wrong?

Where was I going wrong- the quantum dot structure was not neutral. Thanks to @AnoopANair, I was able to find the problem. For anyone having a similar problem look at this video - https://www.youtube....
Parmeet Singh EP 066's user avatar
5 votes

Geometrical Optimization not converging for a double perovskite quantum dot, using Gaussian

I didn't deal with perovskite before, but I got this problem when I used metal atom in my complex. So, from my point of view, I think your calculation needs more cycles to get converged so what about ...
Abd-Elazeem Mohamed's user avatar
5 votes
Accepted

SCF Calculation not converging after two decimal places in Quantum ESPRESSO

My suggestion is that you first get an SCF calculation to converge for this structure before you try relaxing, especially if you aren't sure what you're going to get. Then you can proceed to ...
Brandon Bocklund's user avatar
3 votes

Error while doing a band structure calculation in Quantum ESPRESSO

This may not be the issue, but the manual says the max_seconds keyword under &control is maximum CPU time, not wall time, ...
1 vote

Error in TranSIESTA: "The electrode down-folding region is 0 in the device region"

OP: "Thanks for your follow-up; I've found the answer, so I'm no longer in need of assistance." If anyone including the OP wants to write an answer, let me know in a comment and I'll ...

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