Strange results for: average (electrostatic) potential at core

[hra]

Dear all,

I'm calculating a wurtzite supercell, and noticed something strange in the electrostatic potential. Below are lines from the OUTCAR of two calculations that should be the same.

4 atom unit cell:
average (electrostatic) potential at core
the test charge radii are 1.0314 0.7089
(the norm of the test charge is 1.0000)
1 -28.9420 2 -28.9420 3 -64.1494 4 -64.1494

96 atom supercell (essentially everything is identical to the above system: the band structure is simply folded from the unit, and the total energy is that of the unit multiplied by 24)
average (electrostatic) potential at core
the test charge radii are 1.0314 0.7089
(the norm of the test charge is 1.0000)
1 -28.9406 2 -28.9405 3 -28.9406 4 -28.9406 5 -28.9405
6 -28.9405 7 -28.9405 8 -28.9404 9 -28.9405 10 -28.9405
11 -28.9406 12 -28.9404 13 -28.9405 14 -28.9406 15 -28.9405
16 -28.9406 17 -28.9406 18 -28.9405 19 -28.9406 20 -28.9405
21 -28.9406 22 -28.9405 23 -28.9407 24 -28.9405 25 -28.9405
26 -28.9406 27 -28.9404 28 -28.9405 29 -28.9406 30 -28.9404
31 -28.9405 32 -28.9405 33 -28.9405 34 -28.9405 35 -28.9406
36 -28.9406 37 -28.9406 38 -28.9404 39 -28.9407 40 -28.9405
41 -28.9406 42 -28.9406 43 -28.9406 44 -28.9405 45 -28.9406
46 -28.9405 47 -28.9405 48 -28.9406 49 -63.9864 50 -64.1529
51 -64.1531 52 -64.1531 53 -64.1530 54 -64.1530 55 -64.1530
56 -64.1530 57 -64.1530 58 -64.1530 59 -64.1531 60 -64.1530
61 -64.1531 62 -64.1531 63 -64.1529 64 -64.1529 65 -64.1529
66 -64.1529 67 -64.1530 68 -64.1530 69 -64.1531 70 -64.1529
71 -64.1530 72 -64.1529 73 -64.1532 74 -64.1530 75 -64.1530
76 -64.1530 77 -64.1529 78 -64.1530 79 -64.1530 80 -64.1530
81 -64.1532 82 -64.1530 83 -64.1529 84 -64.1530 85 -64.1529
86 -64.1530 87 -64.1529 88 -64.1530 89 -64.1530 90 -64.1530
91 -64.1529 92 -64.1531 93 -64.1531 94 -64.1529 95 -64.1529
96 -64.1530

Please look at atom number 49 in the supercell. WTF?!?
Interestingly, the average of the average electrostatic potential of atoms 49-96 is -64.149...

Is there something dodgy in the evaluation of these average electrostatic potential at core values printed in the OUTCAR?

Best, Hannes

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