A question about PARCHG

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repent03 · #1 Post by **repent03** » Wed Mar 21, 2012 6:53 am

Dear vasp users

I have done a Band decomposed charge density (patial charge) calculation, and I think the data of grid points refer to the square of absolute values of wavefunctions.

It should all be positive,but I found that there are negative values in PARCHG.

Did I misunderstand something?

Any suggestions are welcomed!

Thanks

Danny · #2 Post by **Danny** » Wed Mar 21, 2012 6:57 pm

Yes you have understood correctly, a density should be positive definite...however (and this is the twist) the densities in the PARCHG file (just as for the CHGCAR file) come from pseudo wavefunctions, which can result in negative densities at the atomic centers (this is due to the construction of PAW). Another source of negative values is just simply noise. You will find in the vacuum reqions spaces where the density oscillates between positive and negative values...these are values that you should consider to be "zero" .

Danny

repent03 · #3 Post by **repent03** » Thu Mar 22, 2012 6:48 am

[quote="Danny"]Yes you have understood correctly, a density should be positive definite...however (and this is the twist) the densities in the PARCHG file (just as for the CHGCAR file) come from pseudo wavefunctions, which can result in negative densities at the atomic centers (this is due to the construction of PAW). Another source of negative values is just simply noise. You will find in the vacuum reqions spaces where the density oscillates between positive and negative values...these are values that you should consider to be "zero" .

Danny[/quote]

Thank you, Danny! It does help me very much!!