problem with Berry phase, calculation of Born effective charge

[aakbarz]

I am trying to redo the test example in VASP manual of NaF for calculating the Born effective charge using Berry phase approach. Unfortunately I could not get any numbers close to what is written in the manual. I used US91 PPS and following are the results for undistorted and distorted lattice and the input parameters, respectively.

Could anyone please let me know what is wrong in my calculations?

Thanks in advance,

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Undistorted lattice:

IGPAR=1
Expectation value term: <R>ev
<R> = ( 0.00000, 0.00000, 0.00000 ) electrons Angst
Berry-Phase term: <R>bp
<R> = ( 0.00000, 0.00000, 0.00000 ) electrons Angst
+( 0.00000, 4.52889, 4.52889 ) *c
ionic term: <R>ion
<R> = ( -6.79333, -6.79333, -6.79333 ) electrons Angst

IGPAR=2
Expectation value term: <R>ev
<R> = ( 0.00000, 0.00000, 0.00000 ) electrons Angst
Berry-Phase term: <R>bp
<R> = ( 0.00000, 0.00000, 0.00000 ) electrons Angst
+( 4.52889, 0.00000, 4.52889 ) *c
ionic term: <R>ion
<R> = ( -6.79333, -6.79333, -6.79333 ) electrons Angst

IGPAR=3
Expectation value term: <R>ev
<R> = ( 0.00000, 0.00000, 0.00000 ) electrons Angst
Berry-Phase term: <R>bp
<R> = ( 0.00000, 0.00000, 0.00000 ) electrons Angst
+( 4.52889, 4.52889, 0.00000 ) *c
ionic term: <R>ion
<R> = ( -6.79333, -6.79333, -6.79333 ) electrons Angst

Distorted lattice:
IGPAR=1
Expectation value term: <R>ev
<R> = ( 0.00000, 0.00000, 0.00018 ) electrons Angst
Berry-Phase term: <R>bp
<R> = ( 0.00000, 0.13717, 0.13741 ) electrons Angst
+( 0.00000, 4.53090, 4.53886 ) *c
ionic term: <R>ion
<R> = ( -6.79635, -6.79635, -7.06060 ) electrons Angst

IGPAR=2
Expectation value term: <R>ev
<R> = ( 0.00000, 0.00000, 0.00018 ) electrons Angst
Berry-Phase term: <R>bp
<R> = ( 0.13717, 0.00000, 0.13741 ) electrons Angst
+( 4.53090, 0.00000, 4.53886 ) *c
ionic term: <R>ion
<R> = ( -6.79635, -6.79635, -7.06060 ) electrons Angst

IGPAR=3
Expectation value term: <R>ev
<R> = ( 0.00003, -0.00003, 0.00018 ) electrons Angst
Berry-Phase term: <R>bp
<R> = ( -0.13717, -0.13717, 0.00000 ) electrons Angst
+( 4.53090, 4.53090, 0.00000 ) *c
ionic term: <R>ion
<R> = ( -6.79635, -6.79635, -7.06060 ) electrons Angst

INCAR parameters in case of Berry phase calculations:

SYSTEM = NaF

restart settings
ISTART = 1
ICHARG = 11

output settings
LCHARG = .TRUE.
LWAVE = .TRUE.

settings for parallel version (ignored in serial run)
NPAR = 4 how many bands in parallel
LPLANE = .TRUE. distribute each wave over processors

setting the Berry phase calculations
LBERRY = .TRUE.
IGPAR = 1
NPPSTR = 6
DIPOL = 0.25 0.25 0.25

Electronic Relaxation 1
NWRTITE = 2; LPETIM = F
PREC = default Medium=default, Low, High; affects ENMAX, mesh, pspot
EDIFF = 1E-06 energy stopping-criterion for electr. iterations
ALGO = Fast

Ionic Relaxation
IBRION = 2
ISIF = 2
NSW = 500 max number of geometry steps
EDIFFG = -1E-02 stopping-criterion for IOM
POTIM = 0.1

ISMEAR = 0
SIGMA = 0.15

For SCF calculation ISIF =3 was chosen and then I copied CONTCAR to POSCAR and reset ISIF=2 for Berry phase calculations. Each time I used CHG and CHGCAR for SCF calculation when I ran VASP for different IGPAR's.
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