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shankar1729 / jdftx

JDFTx: software for joint density functional theory
http://jdftx.org
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Calculation of the electronic structure of 2D materials #337

Open moyulyy opened 3 months ago

moyulyy commented 3 months ago

Dear Shankar

I encountered some doubts when using jdftx to calculate the band structure of two-dimensional graphene-like materials.

  1. How are the weights of the parameters ‘kpoint‘ set? In other words, when there are multiple k-points, what do different or identical weights mean? If the weight is set to zero, does it mean that the K-point has no contribution to the band structure?

  2. The K-points I generated using the ’bandstructKpoints‘ script have the same weight. How does the script determine and give the weight?

  3. I used jdftx to calculate the CBM, VBM and Fermi level of a 2D graphene-like material, but the results do not match those calculated by VASP. How can I correctly compare the band structures of the two software? In other words, does jdftx systematically overestimate or underestimate the band structure calculations relative to vasp? How should I go about understanding or resolving the different results calculated by the two software?

  4. I noticed that calculations using solvation have an effect on the Fermi level of 2D graphene-like materials relative to calculations in vacuum alone. How can I understand the effect of solvation on 2D slabs?

Looking forward to your reply

Best, 
lyy

shankar1729 commented 3 months ago
  1. The weights play no role in a band structure calculation. These only matter for how k-points contribute to density and energy in self-consistent calculations.
  2. That's why the weights are just set to equal by the bandstructKpoints script. (JDFTx still checks that the weights add up to 1, even if they don't get used in the end.)
  3. Are you comparing absolute eigenvalues? If so, these are pseudopotential dependent and not a physical quantity that can be compared. In JDFTx, if you use slab truncation, then you have a well-defined zero reference of potential far away (for a neutral calculation) and the eigenvalues are well-defined and comparable between different pseudopotentials. But these are likely still undefined up to a constant offset in VASP.
  4. Solvation changes the electrostatic potential profile and the alignment of energy levels within the slab/2D material relative to far out in the vacuum/liquid. This is a physical effect that is of interest especially when considering photocatalysis as it impacts connections between band-edge energy levels and reaction potentials. (Please search for solvation effects on band alignment in the literature for more info.)