12

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, there are two types of excitons: opposite spins of electrons will lead to a dark exciton with S=0 (since it doesn't allow for momentum conservation). Same spin ...


9

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 Angstrom is sufficient, but this needs to be tested for your system and property of interest. The trends in many optical and electronic properties (such as ...


9

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 sufficiently not interacting is to increase the cell size and see if your property changes. If it does, repeat again until its converged just like kpoints or energy ...


6

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 conventional DFT methods. This can be fixed to some degree by relaxing your nanoparticle using functionals such as PBE then using a hybrid functional such as HSE06 ...


5

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 converging the numerical settings like the cutoff energies for your properties of interest. I was able to get an SCF calculation to converge using your input file by ...


5

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.com/watch?v=KxO5uLsvkRE\ I have also used 6 Hydrogen atoms which are there to neutralize the extra charge. My new quantum dot looks like this. I Hope, this ...


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