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First of all, thank you for your help! You are so helpful every time.

I would like to calculate the influence of the structural defects on the electronic structure in the HfS2 monolayer. With VESTA software, I created a supercell in which I created a defect. What is important for this type of calculation? How large a supercell guarantees that I have no interactions between individual defects? What traps can I fall into? enter image description here

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First of all, I assume that you are taking VASP to perform your calculation.

Secondly, I assume that your structural defect is taking a Hf atom from your structure. (You can deal with substitutional doping with similar logic.)

Thirdly, for the HfS2 monolayer, there are two phases, namely T-phase and H-phase. The T-phase monolayer was fabricated in the experiment, however, the phonon spectrum indicates that the H-phase monolayer is thermally unstable. So I assume that you are considering the defects problem in T-phase HfS2 monolayer.

What is important for this type of calculation?

  • When the T-phase is doping, you should take the spin-orbit coupling into account due to the broken inversion symmetry and the existence of heavy atom Hf.
  • To simulate HfS2 monolayer, a large vacuum (20 angstroms) should be included along the z-direction.
  • You should relax your doped structure to find the lowest-energy configuration.
  • Defects may induce magnetism in your system, you should make a spin-polarized calculation to verify that.

How large a supercell guarantees that I have no interactions between individual defects?

A $4\times 4\times1$ supercell is enough. You can ref this paper, in which the author investigated the monolayer T-phase PtSe2 with substitutional doping.

What traps can I fall into?

  • Without building supercell.
  • Without consideration of spin-orbit coupling.
  • Without adding enough vacuum along the z-direction.
  • The lattice constant is important, you should take experimental lattice constant to build your model not taking bulk lattice constant.

May helps.

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