dipol+quadrupol energy correction too large

[zsoltrak]

Dear VASP useres,

I'm trying to calculate the (100) surface energy of of ThO2 using slab models. Since the (100) layers are charged (alternating Th and O planes), there is a net dipole moment perpendicular to the slab (z-direction). In order include the dipole corrections for the total energy I set IDIPOL = 3 and carried out the calculations on slabs with increasing thickness. For thin slabs the dipole corrections seem to be reasonable (dipol+quadrupol energy correction 0.246832 eV), but for thicker slabs the corrections jump to unreasonably large values: dipol+quadrupol energy correction 179.223968 eV.
I browsed the forum and the user manual, but I couldn't find an explanation for this behaviour. I would appreciate if somebody could help me with this issue.

Here is my INCAR:

System = ThO2_slab
ISTART = 1
ICHARG = 1
ENCUT = 500
PREC = High

ISPIN = 1
ISMEAR = 0; SIGMA = 0.01
LORBIT = 11

NSW = 60
ISIF = 2
IBRION = 1
EDIFFG = -0.01

LMAXMIX = 6

IDIPOL = 3

and the OUTCAR:

DIPCOR: dipole corrections for dipol
direction 3 min pos 92,
dipolmoment 0.000000 0.000000 31.340853 electrons x Angstroem
Tr[quadrupol] -1676.729050

energy correction for charged system 0.000000 eV
dipol+quadrupol energy correction 179.223968 eV
added-field ion interaction 0.000000 eV (added to PSCEN)


Thank you,
Zsolt

[admin]

please check if the origin of the dipol was kept at reasonable positions for all test you made. Of course the dipol moment increases with increasing slab thickness,