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I treat a system of molecule adsorption on metal surface. I want to calculate the dipole moment of this adsorption system and the change under an external electric field.
In OUTCAR I got the following lines when I caculate the total energy (IDIPOL=3):

DIPCOR: dipole corrections for dipol
direction 3 min pos 215,
dipolmoment 0.000000 0.000000 -1.227354 electrons x Angstroem
Tr[quadrupol] -144489.858937

energy correction for charged system 0.000000 eV
dipol+quadrupol energy correction 0.018698 eV
added-field ion interaction 0.000000 eV (added to PSCEN)........
free energy TOTEN = -1052.984993 eV

but when I change the INCAR as IDIPOL = 3
LDIPOL = .TRUE.
the OUTCAR changes like this:"

DIPCOR: dipole corrections for dipol
direction 3 min pos 237,
dipolmoment 0.000000 0.000000 -0.643487 electrons x Angstroem
Tr[quadrupol] -144488.433825

energy correction for charged system 0.000000 eV
dipol+quadrupol energy correction -0.005140 eV
added-field ion interaction -79.727979 eV (added to PSCEN)

free energy TOTEN = -1052.47499728 eV"

my question is:
1) I have different total energy for LDIPOL=.TRUE. and LDIPOL=.FALSE. which one should I trust and why are they different?
2)is the dipole correction only just an artificial one to cancel the unphysical field coming from finite cell or the true dipole moment of the system?
3) how does VASP calculate the dipole energy correction?
<span class='smallblacktext'>[ Edited ]</span>

@ 1) I do not see that you have two different total energies, I read both times: free energy TOTEN = -1052.47499728 eV
@ 3) see http://cms.mpi.univie.ac.at/vasp/vasp/node136.html and the refernces given there

I'm sorry, I made a mistake when I copied the data from OUTCAR to here and now I'v corrected the data, you see , TOTEN= -1052.984993 when LDIPOL = .FALSE..
thank you for your suggestion about the references