I have created a cif file containing two different organic 2D layers with large vacuum in the z-axis. Previously I've calculated the the band gap of each layer separately using different cif files. But now I need to calculate the band gap of each of these two layers, while they are on top of each other (to see the change). Now if I do scf calculation for theses two layers in a single cif, it will show me the HOMO-LUMO of the entire system and not each layer.
So I wonder how I should approach that, so that it will give me HOMO-LUMO of each layer separately. Thanks!
When you have two layers in a single system (or cif file), it will show you the HOMO and LUMO of the entire system. To see the HOMO, LUMO of each layer, you can calculate the PDOS of all atoms in each layer. It is not a bad approach.
Thanks Dr. Manh-Thuong Nguyen! I know to how to do the PDOS, but I wonder how should I interpret the HOMO-LUMO from there. Can you please give me any suggestions or share recourses links? Thanks again.
When you build a junction (two different layers here) their bands bend at the interface. So bands at the interface are different comparing to single layers. But because the electron waves are de-localized there's not separate HOMO-LUMO for each of them.
Abdullah Al Maruf with QE calculations you can find the Fermi levels of your systems in the output files. Suppose that your 2D organic systems are semiconductors, the Fermi level of each system is in between its valance band maximum (or HOMO if you prefer) and conduction band minimum.
It seems like you have a Van der Waals (or hydrogen bonded) layered system, the interaction between two layers will not change much the PDOS of each layer when they are brought together, maybe, there is an energy shift (if the two layers have different workfunctions).
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