bader charges in bulk GaN

Bader charge density analysis

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Manjusha
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Joined: Wed Jul 29, 2015 1:28 pm

bader charges in bulk GaN

Post by Manjusha »

Hello

I am calculating bader charges from a cube file for hexagonal GaN bulk system. The Ga and N layers in this compound are in the form of : ABA'B'ABA'B'..... where the difference between A and A' layers is that they are slightly shifted laterally with respect to each other. Similarly, the B and B' layers. First, I have generated a charge density cube file by doing post-processing of the wavefunctions collected from the scf calculation of bulk 2x2x2 GaN system in Quantum Espresso. Then I ran the bader code for the cube file to get the charges. The k-point grid I used is 12x12x12 .

The total charge of the system comes out to be correct (the expected valence charge of the system). Also, the charges on atoms of the same layer are same. But the problem is that the charges on Ga atoms of layers A and A' (and also charges on N atoms of layers B and B') are not same. This is a bulk system and all the Ga atoms are in same chemical environment. They are tetrahedrally bonded to 4 N atoms (and same is true for N atoms, N atoms in layers B and B' are tetrahedrally bonded to 4 Ga atoms). So, I expected that the charges on all the Ga atoms in this bulk system should be same. Can someone please tell me what I am missing?

Here is the content from ACF.dat file :

# X Y Z CHARGE MIN DIST ATOMIC VOL
--------------------------------------------------------------------------------
1 18.2640 10.5444 19.7982 11.4266 1.5237 66.6395
2 15.2200 5.2722 19.7982 11.4265 1.5237 66.6358
3 12.1760 10.5444 19.7982 11.4266 1.5237 66.6395
4 9.1320 5.2722 19.7982 11.4266 1.5237 66.6395
5 18.2640 10.5444 3.7320 6.5809 1.7181 92.3652
6 15.2200 5.2722 3.7320 6.5809 1.7181 92.3652
7 12.1760 10.5444 3.7320 6.5809 1.7181 92.3652
8 9.1320 5.2722 3.7320 6.5809 1.7181 92.3652
9 3.0428 1.7567 4.9495 11.3747 1.5089 64.9901
10 9.1308 1.7567 4.9495 11.3747 1.5089 64.9901
11 6.0868 7.0289 4.9495 11.3747 1.5088 64.9901
12 12.1748 7.0289 4.9495 11.3747 1.5089 64.9901
13 3.0428 1.7567 8.6815 6.6179 1.7392 93.7406
14 9.1308 1.7567 8.6815 6.6179 1.7393 93.7406
15 6.0868 7.0289 8.6815 6.6179 1.7392 93.7461
16 12.1748 7.0289 8.6815 6.6179 1.7392 93.7461
17 18.2640 10.5444 9.8991 11.4265 1.5237 66.6339
18 15.2200 5.2722 9.8991 11.4265 1.5237 66.6358
19 12.1760 10.5444 9.8991 11.4265 1.5237 66.6339
20 9.1320 5.2722 9.8991 11.4265 1.5237 66.6358
21 18.2640 10.5444 13.6310 6.5809 1.7181 92.3652
22 15.2200 5.2722 13.6310 6.5809 1.7181 92.3652
23 12.1760 10.5444 13.6310 6.5809 1.7181 92.3652
24 9.1320 5.2722 13.6310 6.5809 1.7181 92.3652
25 3.0428 1.7567 14.8486 11.3747 1.5089 64.9901
26 9.1308 1.7567 14.8486 11.3747 1.5089 64.9901
27 6.0868 7.0289 14.8486 11.3747 1.5088 64.9901
28 12.1748 7.0289 14.8486 11.3747 1.5089 64.9901
29 3.0428 1.7567 18.5806 6.6179 1.7392 93.7424
30 9.1308 1.7567 18.5806 6.6178 1.7393 93.7388
31 6.0868 7.0289 18.5806 6.6178 1.7392 93.7388
32 12.1748 7.0289 18.5806 6.6178 1.7392 93.7388
--------------------------------------------------------------------------------
VACUUM CHARGE: 0.0000
VACUUM VOLUME: 0.0000
NUMBER OF ELECTRONS: 288.0005

I expected that the charges on Ga atoms having numbers 1,2,3,4 ; 9,10,11,12 ; 17,18,19,20 ; 25,26,27,28 should all be same. Same should be true for N atoms.

The z-valence in the pseudopotential file for Ga and N are 13 and 5 respectively.

Thank you in advance.
Manjusha
IIT Kanpur, India
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