Very confusing description of the unit in VESTA Manual for an imported VASP CHGCAR file

[Yong Han]

From the VESTA Manual, I can find this description:

"CHG stores lattice vectors, atomic coordinates, and total charge densities multiplied by the unit-cell volume, V . PAW one-center occupancies are added to them in CHGCAR. ...... When these files are read in to visualize isosurfaces and sections, data values are divided by V in the unit of bohr^3. The unit of charge densities input by VESTA is, therefore, bohr^3."

I also found such description for a VASP CHACAR file elsewhere:
"The values in the CHGCAR are written in terms of the charge density rho(r) (given in electrons/angstroms^3) multiplied by the volume of your supercell V (given in angstroms^3)." Thus, the unit in CHGCAR should be (electrons/angstroms^3)*V.

When I use VESTA "Volumetric data" to import a VASP CHGCAR file, if I choose the first  option "Raw Data (do nothing)" in the column "Convert the unit", what is the unit of the imported data? That is, the unit of the imported data is still " (electrons/angstroms^3)*V" (according to the above description for a VASP CHACAR file) or bohr^3 (according to the above description in the VESTA Manual for reading a VASP CHACAR file)?

[Koichi Momma]

The documentation and GUI of VESTA might not be very clear.

When reading CHGCAR files, VESTA interprets its values in the unit of electrons/bohr^3.
This is the default code.

If you choose "Raw Data (do nothing)", the unit will still be electrons/bohr^3.
Other than file format of CHGCAR, this option really does nothing but in the case of CHGCAR, it means, "don't do extra conversion".

Best regards,
Koichi

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Koichi Momma
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[Yong Han]

Thank you very much for your response! This makes sense.

[KK M]

Dr Koichi Momma,

1. That means the 'Unit' of Isosurface value we select in CHGCAR or charge density difference visualisation is electrons/bohr^3 ? 

2. For example isosurface value selected is say 0.006, and it shows some 3D visuals of Yellow and Cyan colors. Now, the volumetric space within these 3D colors are all having 'charge density greater than 0.006 electrons/bhor^3. and the remaining volumetric space (empty) i.e. above of these volumes is less than 0.006 electrons/bhor^3. Is this understanding correct?  

Thanking you.

Regards

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[Koichi MOMMA]

Yes, that's correct. But if you see cyan isosurfaces, that part has negative density (-0.0006 )

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[KK M]

Thank you Dr Koichi Momma.

hmm. further doubt now, please.

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in general the Cyan is considered as 'charge depletion' region. So, the '-ve' sign you mentioned is just to indicate that the charge density in that Cyan region is 'depleted' or 'short of' such isosurface value i.e in this example 0.006 electrons/Bhor^3. Is that correct? 

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Regards

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