Band decomposed charge density

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Discussion Overview

The discussion revolves around the concept of band decomposed charge density, particularly in the context of ground state properties of conduction bands in materials. Participants explore the implications of charge density calculations in relation to filled and unfilled bands, with references to specific literature and computational parameters in VASP.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses confusion regarding the presence of band decomposed charge density in the conduction band when the system is in the ground state, suggesting that there should be no charges or electrons.
  • Another participant asserts that the conduction band is not necessarily empty in the ground state, particularly in metals, and argues that charge density can be calculated regardless of whether an orbital is filled.
  • A participant provides a link to the relevant figure from the literature to support the discussion.
  • There is a question raised about the difference between "the charge density" and "the total charge density" in the context of VASP parameters, specifically regarding the inclusion of unoccupied bands in calculations.

Areas of Agreement / Disagreement

Participants do not reach a consensus; there are competing views regarding the nature of charge density in conduction bands and the implications of computational parameters in VASP.

Contextual Notes

Some assumptions about the behavior of conduction bands in different materials (e.g., metals vs. insulators) are not explicitly stated, and the discussion does not resolve the differences in terminology related to charge density calculations.

Douasing
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Hi,there are many literatures concered with band decomposed charge density(As an example,see FIG.3 in PHYSICAL REVIEW B 78, 235430 2008).
For condution band,there should not be charges or electrons when the system is in the ground state,but,those literares still show a band decomposed charge density picture,I'm very confused with that.
Douasing
 
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Do you have a link for that figure? I can find it in google, but it's not available for free.
 
Of course. The link is http://journals.aps.org/prb/pdf/10.1103/PhysRevB.78.235430
And the FiG.3 is shown as follows:
upload_2014-12-15_12-34-48.png

FIG. 3. Color online Band decomposed charge density at the Gamma
point for 13,0, 14,0, and 16,0.
 
Last edited by a moderator:
In general, the conduction band isn't empty, not even in the ground state, especially in metals. So I don't see a reason as why not to calculate charge density. The pictures you are showing is the electron density $$ |\psi|^2$$ as would result from a single Bloch function or orbital being filled. Obviously, you can plot it irrespective of whether the orbital is filled or not.
 
DrDu said:
In general, the conduction band isn't empty, not even in the ground state, especially in metals. So I don't see a reason as why not to calculate charge density. The pictures you are showing is the electron density $$ |\psi|^2$$ as would result from a single Bloch function or orbital being filled. Obviously, you can plot it irrespective of whether the orbital is filled or not.
In VASP, there is a parameter called NBMOD as follows:
NBMOD=0 : Take all bands to calculate "the charge density", even unoccupied bands are taken into account.
NBMOD=-1: Calculate the "total charge density" as usual. This is the default value if nothing else is given.
What's the difference bewteen "the charge density" and "the total charge density" ?
 

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