Ionic Contribution in BECT of NaF by Berry Phase Method

[kjt0314]

Dear admin and vasp users

Concerning vasp5 manual p88

In the vasp example ,
With IGPAR = 1 for the distorted,
Berry-Phase term: <R>bp
<R> = ( 0.00000, 0.17982, 0.17982 ) electrons Angst
ionic term: <R>ion
<R> = ( 20.29590, 20.29590, 19.98019 ) electrons Angst

In my calculation with vasp5.2/PAW_PBE
With IGPAR = 1 for the distorted,
e<r>_bp=( 0.00000 0.17975 0.17975 ) e*Angst
ionic dipole moment:
p[ion]=( -6.76530 -6.76530 -7.08101 ) e*Angst

=>>
The Berry phase terms are similar between the two calcualtions(seems OK).

However, the ionic terms differ as frequently met in other people's postings.
The value(20.29590) in the example corresponds to my results when it is multiplied by 3 (-6.76530*3 = -20.29590).
Q1: Why are the amplitudes different as much as three times ?
In addition the signs are opposite each other (+ for the example vs - for my results).
Q2: Why are the signs opposite ?

Is there anyone who explain these two problems?
And I think that the vasp administrator needs to specify the INCAR file related to the example in order to avoid these kind of problems about Berry Phase Method and BECT

my INCAR
SYSTEM = NaF
ISTART = 0
ICHARG = 11
PREC = Accurate
ENMAX = 400
ISMEAR = 0 ; SIGMA = 0.1
EDIFF = 1E-4
NELMIN = 8
LBERRY = .TRUE.
IGPAR = 1
NPPSTR = 6
DIPOL = 0.25 0.25 0.25

I used the same KPOINTS and POSCAR files as the example.

Thanks in advance

With best regards
Jongtaek Kim





<span class='smallblacktext'>[ Edited ]</span>

[admin]

please read the part about the indeterminacy of the Berry Phase terms in the manual

[kjt0314]

Then, how can I reproduce the same results as in the manual.