Valence charge and total charge

Bader charge density analysis

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sambader
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Joined: Wed Sep 06, 2017 3:31 pm

Valence charge and total charge

Post by sambader » Wed Sep 06, 2017 4:02 pm

Dear graeme,
I am just trying to analyse the charge density I've got from vasp for CaTiO3. And here are the ACF.dat and BCF.dat I get when using just the valence charge (bader CHGCAR):
ACF.dat:
# X Y Z CHARGE MIN DIST ATOMIC VOL
--------------------------------------------------------------------------------
1 0.0000 0.0000 0.0000 0.0118 0.3346 0.4624
2 1.9479 1.9479 1.9479 1.5564 0.7869 6.6474
3 1.9479 1.9479 0.0000 7.4773 1.0551 17.3380
4 1.9479 0.0000 1.9479 7.4773 1.0551 17.3380
5 0.0000 1.9479 1.9479 7.4773 1.0551 17.3380
--------------------------------------------------------------------------------
VACUUM CHARGE: 0.0000
VACUUM VOLUME: 0.0000
NUMBER OF ELECTRONS: 24.0000
BCF.dat:
# X Y Z CHARGE ATOM DISTANCE
-------------------------------------------------------------------------
1 0.0000 0.0000 0.0000 0.0118 1 0.0000
2 1.9479 1.9479 1.9479 1.5564 2 0.0000
3 0.0000 1.9479 1.9479 7.4773 5 0.0000
4 1.9479 0.0000 1.9479 7.4773 4 0.0000
5 1.9479 1.9479 0.0000 7.4773 3 0.0000
-------------------------------------------------------------------------
But if I run bader taking into account the valence and the core charge (chgsum.pl AECCAR0 AECCAR2 which gives CHGCAR_sum) bader CHGCAR -ref CHGCAR_sum I get the files:
ACF.dat:
# X Y Z CHARGE MIN DIST ATOMIC VOL
--------------------------------------------------------------------------------
1 0.0000 0.0000 0.0000 0.4925 1.2626 13.0060
2 1.9479 1.9479 1.9479 2.2237 0.9739 8.3651
3 1.9479 1.9479 0.0000 7.0946 0.8928 12.5842
4 1.9479 0.0000 1.9479 7.0946 0.8928 12.5842
5 0.0000 1.9479 1.9479 7.0946 0.8928 12.5842
--------------------------------------------------------------------------------
VACUUM CHARGE: 0.0000
VACUUM VOLUME: 0.0000
NUMBER OF ELECTRONS: 24.0000
BCF.dat:
# X Y Z CHARGE ATOM DISTANCE
-------------------------------------------------------------------------
1 0.0000 0.0000 0.0000 0.4925 1 0.0000
2 0.0000 1.9479 1.9479 7.0946 5 0.0000
3 1.9479 1.9479 1.9479 2.2237 2 0.0000
4 1.9479 0.0000 1.9479 7.0946 4 0.0000
5 1.9479 1.9479 0.0000 7.0946 3 0.0000
-------------------------------------------------------------------------
So as you can see, in both cases, the ACF.dat and BCF.dat are exactly the same....But the problem is that I don't understand why the charge is so different when including the core charge? does this mean some thing ? or should it be a problem some where in the vasp calculated/converged charges: CHGCAR and AECCAR0 AECCAR2?
Many many thanks,
Samir

graeme
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Location: University of Texas at Austin
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Re: Valence charge and total charge

Post by graeme » Thu Sep 07, 2017 5:12 am

The reason that the ACF and BCF files are the same is that in both cases you have just a single charge density maximum at each atomic center, which is good.

The second calculation, when you analyze the total charge, is more accurate, and the results that you should use. Simply, that Bader analysis should be based upon the total charge. Using just the valence charge can give results that are possibly close, but also possibly completely different from that based upon the total charge. How different these are depends upon how many electrons are considered as valence and how ionic you system is.

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