Why do CHGCAR have negative charge?

Message

Benton · #1 Post by **Benton** » Thu Apr 24, 2008 12:05 pm

Dear admin,
I found that there were some negative values in CHGCAR file in some cases. I plotted out charge density in a plane and the negative charge was near atomic centers. Why could it exist?

As far as I know, charge density is the norm of wavefunctions. so I guess the negative values are due to specific normalization method in vasp.

Benton

forsdan · #2 Post by **forsdan** » Thu Apr 24, 2008 5:12 pm

You may already be aware of this but have you made sure you are plotting the correct values? In the case of spin-polarized calculations, the magnetization density (spin up minus spin down) is written to the CHGCAR as well. This quantity can of course be negative. Just a thought.

Best regards,
/Dan Fors

Benton · #3 Post by **Benton** » Fri Apr 25, 2008 1:27 am

I am sure the negative charge density appears in CHGCAR(whether you plot it or not) without spin-polarized. However, the total chrage is normalized. GeSn zinc-blende structure with lattice constant 6.0 Ang. is a simple example. Here, I use PAW-LDA pseuopotential without d electron.

Best,
Benton

somesh · #4 Post by **somesh** » Fri Mar 15, 2013 11:43 am

dear VASP Users,
I faced the same problem with Al. At the atomic centers, some negative charge was observed. The calculation was performed with PAW-PBE for Al.
However, when I used the POTCAR from Al_h(i.e. the hard PP) there was no negative value in the CHGCAR.

Somesh

Danny · #5 Post by **Danny** » Fri Mar 15, 2013 3:30 pm

This is normal for PAW charges. In the core region the electron density is replaced by a "pseudo" density, which can become negative (especially for heavy atoms).

This is a nasty aspect of the CHGCAR files when you have to work with the charges. The obtained profiles are correct, as long as you stay far enough away from the nucleus. Furthermore, when you integrate these radial densities they will integrate to the correct number of electrons (which is a nice thing).

If you are interested in the radial densities you can get from VASP you can have a look in these two papers:
http://onlinelibrary.wiley.com/doi/10.1 ... 8/abstract
and
http://onlinelibrary.wiley.com/doi/10.1 ... 3/abstract

I did not explicitly include exaples where the core density becomes negative (this would be to shocking to most, but when you read the PAW publications it becomes clear how this is possible.

Danny