21
votes
Accepted
How to understand the time-reversal symmetry in graphene?
Two-band model for graphene. To simplify the discussion of Dirac points, it is sufficient to consider a nearest-neighbor tight-binding 2-band model for graphene. This is a spinless model because spin-...
- 10.9k
16
votes
How to explain to a five year old why "DFT with local exchange–correlation functionals do(es) not describe van der Waals interactions accurately"?
Standard DFT functionals are based exclusively on local information, e.g. for a GGA functional
$$ E_{xc} = \int n({\bf r}) \epsilon_{xc}(n({\bf r}), \nabla n({\bf r})) {\rm d}^3r $$
while van der ...
- 18k
14
votes
Accepted
Why is the band gap of graphene "opened" in this VASP calculation?
The reason why graphene has Dirac points at K and $-$K is because of a combination of time reversal and inversion symmetries. Therefore, if you impose these symmetries in your VASP calculation, there ...
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10
votes
How to explain to a five year old why "DFT with local exchange–correlation functionals do(es) not describe van der Waals interactions accurately"?
I'll turn my comment as an answer, as requested by the OP and Nike.
Susi Lehtola's answer has already pointed out that dispersion (which may be a more accurate term than van der Waals interaction here)...
- 9,076
10
votes
Accepted
What's the past and future of 2D materials since graphene?
Actually, if you allow for quasi-2D systems, graphene has had a recent renaissance starting with the experimental discovery of correlated states in "magic angle" twisted bilayer graphene, ...
- 4,711
10
votes
Why can't I reproduce the behavior of an H-saturated graphene flake?
From the available information, I think it is caused by the small value of $T_{damp}$. This causes the $T$ to fluctuate wildly, which can induce unwanted bond-breaking. Best practise is to keep $T_{...
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10
votes
DFT vs tight-binding solutions for a Dirac cone in graphene: Why is the DFT version squeezed?
Oh! I found the answer already. Since I'm doing the calculation along the High symmetry point. Im doing the calculation along G -> K -> M -> G, that's why the right hand sides show such phenomena. In ...
- 2,793
10
votes
Accepted
What does capital sigma followed by an integer (Σn) mean in the context of grain boundaries?
The $\Sigma$ values represent the volume of the Coincident Site Lattice (CSL) of the grain boundary in terms of the volume of the unit cell of the crystal. In general, grain boundaries with higher ...
- 1,349
10
votes
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How accurate is DFTB+ in reproducing DFT result?
The DNA-graphene interaction is only weak when there is no considerable charge transfer between them. Now you have many aryl radicals in your graphene, and aryl radicals are electron-deficient ...
- 9,076
8
votes
Accepted
Simulated STM Image with Quantum-ESPRESSO's pp.x
A minimal input file
For simulated STM, you can use pp.x. A minimal input file might look like this:
...
- 2,131
7
votes
Accepted
Binding energy calculation for Zn atom on armchair graphene slab?
As mentioned by @Camps in the comments, the Zn reference used in the paper is almost certainly that of an isolated Zn atom in the gas phase.
If I understand correctly from briefly scanning the paper, ...
- 2,544
6
votes
How to separate the band structure of different materials in heterostructures using Quantum ESPRESSO?
I believe what you are referring to is a "projected" or "fat" band structure diagram. By assigning colors (or line thickness) to a basis on which you project the Kohn-Sham states (...
- 3,081
6
votes
Does the Mermin-Wagner theorem influence the stability of graphene?
This Physics Stack Exchange thread answers this question very well.
Apparently, the length scale of such "logarithmic divergence" is actually merely in the order of atomic distances even if ...
- 671
5
votes
Help with understanding topologically-protected edge states in domain wall systems
I think my understanding on this problem has improved somewhat. Let me try to clarify my confusions. If anyone sees issues with this reasoning, please let me know.
The idea of phases in this context ...
4
votes
Wavefunction magnitudes being degenerate everywhere on parameter space even though energy degeneracies occur at isolated points?
This is a somewhat handwaving answer but I think it gets the main point across:
We should start by pointing out that the two components of your eigenstates represent the wave function amplitudes on ...
- 2,544
3
votes
Accepted
Theoretical Capacity of g-C3N4?
I guess your citation is from this article : Shangqi Sun et al. and the formula is correct, the calculated value could have been right if the graphitic $\text{g-C3N4}$ had the same structure as ...
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3
votes
Has there been research on improving the strength of graphene-based materials?
There has indeed been quite a lot of research in this area, as is readily uncovered by searching for "improving the strength of graphene" in your search engine of choice; for example, this ...
- 6,647
3
votes
Accepted
Help with definitions in k-space twisted bilayer graphene model
I don't think I can use this Hamiltonian to recover the band structure. The band structure should use a tight-binding Hamiltonian with several unit cells. A colleague told me that this Hamiltonian is ...
2
votes
How to stack a nanocrystal on top of a graphene slab in ASE?
To stack two 2D structures in ASE, a matching of the two unit cells is required. I will assume your graphene and TMD unit cells have the same $\alpha$, $\beta$, $\gamma$ lattice parameters but ...
- 1,550
2
votes
Accepted
Convergence issues in DFTB+ calculations?
I had posted the same question on the dftb+ forum and Prof. Aradi responded to the question with the following answer.
A common strategy is for large metallic systems to start with
a very high ...
- 2,782
2
votes
Accepted
Transiesta with siesta version 4.1.5 not converging
The primary reason why convergence problems occur in TranSiesta is because of not properly testing the screening layers towards the electrodes. I also believe this is your main problem.
Again, ...
- 3,084
1
vote
Number of electrons per cell
I did some searching and found that a unit cell of graphene contains two atoms, with each each hexagonal mer consisting of 6 atoms of carbon.
There's a helpful diagram here:
https://chemistry....
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1
vote
Accepted
Why can graphene nanoribbons be safely used as electrdes, despite having a finite band gap?
From the tutorial it is obvious that the GNR used is metallic, i.e. has no band-gap.
Please see the transmission functions at the end: http://dipc.ehu.es/frederiksen/tstutorial/index.php/...
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