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I trying to calculate x-y plane averaged charge density in 3-D HfO2 slab structure. Actually, for the local permittivity calculation, I need to get the local polarization(x-y averaged) from induced charge density. For getting accurate result, the charge density value within 1E-7 error is necessary.

Anyway I want to get the charge density value within 1E-7 accuracy. Is this possible?

If I set the 'PREC = High', ROPT should be accuracy 2E-4.
(maybe I think this setting is maxium limit for accurate precision)
So, I tried to set 'ROPT = 1E-7 1E-7 (for 2 species Hf, O)'
, but error messages are occured like below

REAL_OPT: internal ERROR: -16 -16 -128 82
REAL_OPT: internal ERROR: -16 -16 -128 82
REAL_OPT: internal ERROR: -16 -16 -128 82
REAL_OPT: internal ERROR: -16 -16 -128 82
LDA part: xc-table for Ceperly-Alder, standard interpolation
REAL_OPT: internal ERROR: -16 -16 -128 82
POSCAR, INCAR and KPOINTS ok, starting setup
REAL_OPT: internal ERROR: -16 -16 -128 82
REAL_OPT: internal ERROR: -16 -16 -128 82
REAL_OPT: internal ERROR: -16 -16 -128 82
WARNING: small aliasing (wrap around) errors must be expected
REAL_OPT: internal ERROR: -16 -16 -128 82
REAL_OPT: internal ERROR: -16 -16 -128 82
REAL_OPT: internal ERROR: -16 -16 -128 82
REAL_OPT: internal ERROR: -16 -16 -128 82
REAL_OPT: internal ERROR: -16 -16 -128 82
REAL_OPT: internal ERROR: -16 -16 -128 82


So, How can I get the accuracy 1E-7 in the charge density calculation?

Should I change NGX,Y,Z manually?
<span class='smallblacktext'>[ Edited ]</span>

I same the same questions .
Any suggestions .