7
$\begingroup$

Rephrasing the above, what is the pattern in which the electron-density data is stored in the CHGCAR file?

I understand that the electron density data in a CHGCAR file is in the form of a 3D Fortran array, but I believe that such electron density data should be stored in 3 columns (NX,NY,NZ). Instead we see the presence of 5 columns. What I am requesting, is a comprehensive description of the 5-column electron density data present in every CHGCAR file, and the significance of every column present to represent the electron-density data.

I have shown the part of the CHGCAR data that I am referring to, is shown below:

  64   64   64
 0.27296628474E+03 0.27129538645E+03 0.26632236747E+03 0.25816527382E+03 0.24701868651E+03
 0.23315320780E+03 0.21691723332E+03 0.19873896341E+03 0.17912393717E+03 0.15864307047E+03
 0.13790873569E+03 0.11754046377E+03 0.98125176377E+02 0.80177959210E+02 0.64108387081E+02
 0.50195641939E+02 0.38574367354E+02 0.29232778335E+02 0.22024079253E+02 0.16690923309E+02
 0.12900228129E+02 0.10283187627E+02 0.84752878195E+01 0.72047216409E+01 0.63226226628E+01
 0.57166613639E+01 0.53025284991E+01 0.50199593897E+01 0.48277275324E+01 0.46988015018E+01
 0.46162530737E+01 0.45701256193E+01 0.45552760083E+01 0.45701256193E+01 0.46162530737E+01
 0.46988015018E+01 0.48277275324E+01 0.50199593897E+01 0.53025284991E+01 0.57166613639E+01
 0.63226226628E+01 0.72047216409E+01 0.84752878195E+01 0.10283187627E+02 0.12900228129E+02
 0.16690923309E+02 0.22024079253E+02 0.29232778335E+02 0.38574367354E+02 0.50195641939E+02
 0.64108387081E+02 0.80177959210E+02 0.98125176377E+02 0.11754046377E+03 0.13790873569E+03
 0.15864307047E+03 0.17912393717E+03 0.19873896341E+03 0.21691723332E+03 0.23315320780E+03
 0.24701868651E+03 0.25816527382E+03 0.26632236747E+03 0.27129538645E+03 0.27129538645E+03
..................... over a hundred thousand lines of data
$\endgroup$
1
6
$\begingroup$

From the Vaspwiki, the CHGCAR file writes out the density using this Fortran snippet:

WRITE(IU,FORM) (((C(NX,NY,NZ),NX=1,NGXF),NY=1,NGYF),NZ=1,NGZF)

Basically, this will iterate through the coordinates in the order X, then Y, then Z. For your case, this would look something like with $(N_x,N_y,N_z)$: $(1,1,1),(2,1,1),...,(64,1,1),(1,2,1),(2,2,1),...$

The five columns don't have any particular meaning, the screen would just become too cluttered if you tried to include more values per line, so they just print five at a time. This is what the FORM option in the code above is doing; they don't include the code for the format on the Vaspwiki, but if the code were just write(iu,*), it would try to print all these values on one line until it ran out of buffer space.

To find the actual coordinate values of a grid point from its index, you can convert using $$(N_x,N_y,N_z)=\frac{N_x-1}{N_{GXF}}\vec{a}+\frac{N_y-1}{N_{GYF}}\vec{b}+\frac{N_z-1}{N_{GZF}}\vec{c}$$ where $\vec{a},\vec{b},\vec{c}$ are the lattice vectors.

$\endgroup$
4
  • $\begingroup$ Okay, then how does VESTA rearrange the data to visualize it? $\endgroup$ – Pranoy Ray Jun 22 at 19:07
  • 1
    $\begingroup$ @PranoyRay I don't know about VESTA and it potentially could warrant another question. But I suspect it just reads the values from the CHGCAR into a 3D array and performs whatever visualization with this data. Is there something missing from my description that you think would be needed to visualize the density? $\endgroup$ – Tyberius Jun 22 at 19:16
  • $\begingroup$ Thank you for your comment. Your answer is perfect. $\endgroup$ – Pranoy Ray Jun 22 at 19:23
  • 1
    $\begingroup$ Since this discussion warrants another question, I have posted it here: mattermodeling.stackexchange.com/questions/6225/… $\endgroup$ – Pranoy Ray Jun 22 at 19:44
1
$\begingroup$

VESAT can understand the data format of CHGCAR outputted by VASP. You just need to move CHGCAR to CHGCAR.vasp and then open with VESTA.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.