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I am using vasp 4.6 to calculate Born effective charge for fluorine in NaF.
In manual, you have asked to use 4*4*4 Monkhorst-Pack sampling of the Brillouin zone. But it is not working and showing the error as follows:

VERY BAD NEWS! internal error in subroutine IBZKPT:
Fatal error: unable to match k-point! 0
So I have change Monkhorst-Pack to 3*3*3. And its working. Using this thing I try to reproduce results for NaF.

I ran the following example taken from the manual

INCAR file
-------
SYSTEM = NaF

NWRITE = 2
ISTART = 0
ISPIN = 2
ENCUT = 400
ICHARG= 1
NPAR=1
IBRION = 2
!POTIM = 0.5
! LREAL= Auto
ALGO = normal
LREAL=.FALSE.
! LORBIT = 10
INIWAV = 1
IALGO = 48 ! uncomment this line to get timings
DOS related values:
ISMEAR = -5 ; SIGMA = 0.1
EMIN = -10 ; EMAX = 15
LBERRY = .TRUE.
IGPAR = 1
NPPSTR = 6
DIPOL = 0.25 0.25 0.25

KPOINTS file
--------------------

NaF
0
Monkhorst
3 3 3
0. 0. 0.


POSCAR
-------------
NaF
4.5102
0.0 0.5 0.5
0.5 0.0 0.5
0.5 0.5 0.0
1 1
Direct
0.0000000000000000 0.0000000000000000 0.0000000000000000
0.5000000000000000 0.5000000000000000 0.500000000000000


I have used the PAW poteintals

The output that I get are not matching with that shown in the manual. Below is my output

Undist:
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
ionic term: <R>ion
<R> = ( -6.76530, -6.76530, -6.76530 ) electrons Angst

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
ionic term: <R>ion
<R> = ( -6.76530, -6.76530, -6.76530 ) 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
ionic term: <R>ion
<R> = ( -6.76530, -6.76530, -6.76530 ) electrons Angst

After that I modified POSCAR file as
NaF
4.5102
0.0 0.5 0.5
0.5 0.0 0.5
0.5 0.5 0.0
1 1
Direct
0.0000000000000000 0.0000000000000000 0.0000000000000000
0.5100000000000000 0.5100000000000000 0.5100000000000000

the OUTPUT file:

dist:
IGPAR=2
Expectation value term: <R>ev
<R> = ( 0.00000, 0.00000, 0.00000 )
Berry-Phase term: <R>bp
<R> = ( 0.08988, 0.00000, 0.08988 ) electrons Angst
ionic term: <R>ion
<R> = ( -6.76530, -6.76530, -7.08101 ) electrons Angst

IGPAR=1
Expectation value term: <R>ev
<R> = ( 0.00000, 0.00000, 0.00002 ) electrons Angst
Berry-Phase term: <R>bp
<R> = ( 0.00000, 0.08988, 0.08988 ) electrons Angst
ionic term: <R>ion
<R> = ( -6.76530, -6.76530, -7.08101 ) electrons Angst

IGPAR =3
Expectation value term: <R>ev( -6.76530, -6.76530, -6.76530 ) electrons Angst

<R> = ( 0.00000, 0.00000, 0.00002 ) electrons Angst
Berry-Phase term: <R>bp
<R> = ( -0.08988, -0.08988, 0.00000 ) electrons Angst
ionic term: <R>ion
<R> = ( -6.76530, -6.76530, -7.08101 ) electrons Angst

Calculation:
1.<R>ev,undist = (0 ,0 ,0 )
2.<R>bp,undist = (0 ,0 ,0 )
3.<R>ion,undist = ( -6.76530, -6.76530, -6.76530 )
4.<R>ev,dist = (0 ,0 ,0 )
5.<R>bp,dist = ( 0.0, 0.0, 0.17976)
6.<R>ion,dist = ( -6.76530, -6.76530, -7.08101 )

As (<R>ev,undist), (<R>bp,undist) is equal to zero, the total change in polarization
is reduced to
delta <R>=(<R>ev+<R>bp)+(<R>ion,dist-<R>ion,undist)
= 0.0000 + 0.17976 +(-7.08101 - (-6.76530))
= -0.31571 electrons/Ã….

It's not matching at all with calculated delta <R>. Please tell me what is the problem with my calculation.

How could one decide this F-sublattice displacement value(0.045102 Ã…)?

Any body would like to focus light on this topic.

thanks in advance,

only the Berry phase terms differ, please check whether this might be due to the indeterminacy of the Berry phase term.
concerning the displacement: simply calculate the positions of the ions in carthesian coordinates and you will see yourself....

Hi Admin,

I am using the exact same approach as suggested in VASP manual but I am getting the same results as Pati.
Additionally I use Vasp 5.2 and PAW-LDA.
Could you please elaborate what exactly do you mean by indeterminacy of the Berry phase term.

Thank you in anticipation.

[quote author= NaF

NWRITE = 2
ISTART = 0
ISPIN = 2
ENCUT = 400
ICHARG= 1
NPAR=1
IBRION = 2
!POTIM = 0.5
! LREAL= Auto
ALGO = normal
LREAL=.FALSE.
! LORBIT = 10
INIWAV = 1
IALGO = 48 ! uncomment this line to get timings
DOS related values:
ISMEAR = -5 ; SIGMA = 0.1
EMIN = -10 ; EMAX = 15
LBERRY = .TRUE.
IGPAR = 1
NPPSTR = 6
DIPOL = 0.25 0.25 0.25

KPOINTS file
--------------------

NaF
0
Monkhorst
3 3 3
0. 0. 0.


POSCAR
-------------
NaF
4.5102
0.0 0.5 0.5
0.5 0.0 0.5
0.5 0.5 0.0
1 1
Direct
0.0000000000000000 0.0000000000000000 0.0000000000000000
0.5000000000000000 0.5000000000000000 0.500000000000000


I have used the PAW poteintals

The output that I get are not matching with that shown in the manual. Below is my output

Undist:
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
ionic term: <R>ion
<R> = ( -6.76530, -6.76530, -6.76530 ) electrons Angst

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
ionic term: <R>ion
<R> = ( -6.76530, -6.76530, -6.76530 ) 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
ionic term: <R>ion
<R> = ( -6.76530, -6.76530, -6.76530 ) electrons Angst

After that I modified POSCAR file as
NaF
4.5102
0.0 0.5 0.5
0.5 0.0 0.5
0.5 0.5 0.0
1 1
Direct
0.0000000000000000 0.0000000000000000 0.0000000000000000
0.5100000000000000 0.5100000000000000 0.5100000000000000

the OUTPUT file:

dist:
IGPAR=2
Expectation value term: <R>ev
<R> = ( 0.00000, 0.00000, 0.00000 )
Berry-Phase term: <R>bp
<R> = ( 0.08988, 0.00000, 0.08988 ) electrons Angst
ionic term: <R>ion
<R> = ( -6.76530, -6.76530, -7.08101 ) electrons Angst

IGPAR=1
Expectation value term: <R>ev
<R> = ( 0.00000, 0.00000, 0.00002 ) electrons Angst
Berry-Phase term: <R>bp
<R> = ( 0.00000, 0.08988, 0.08988 ) electrons Angst
ionic term: <R>ion
<R> = ( -6.76530, -6.76530, -7.08101 ) electrons Angst

IGPAR =3
Expectation value term: <R>ev( -6.76530, -6.76530, -6.76530 ) electrons Angst

<R> = ( 0.00000, 0.00000, 0.00002 ) electrons Angst
Berry-Phase term: <R>bp
<R> = ( -0.08988, -0.08988, 0.00000 ) electrons Angst
ionic term: <R>ion
<R> = ( -6.76530, -6.76530, -7.08101 ) electrons Angst

Calculation:
1.<R>ev,undist = (0 ,0 ,0 )
2.<R>bp,undist = (0 ,0 ,0 )
3.<R>ion,undist = ( -6.76530, -6.76530, -6.76530 )
4.<R>ev,dist = (0 ,0 ,0 )
5.<R>bp,dist = ( 0.0, 0.0, 0.17976)
6.<R>ion,dist = ( -6.76530, -6.76530, -7.08101 )

As (<R>ev,undist), (<R>bp,undist) is equal to zero, the total change in polarization
is reduced to
delta <R>=(<R>ev+<R>bp)+(<R>ion,dist-<R>ion,undist)
= 0.0000 + 0.17976 +(-7.08101 - (-6.76530))
= -0.31571 electrons/Ã….

It's not matching at all with calculated delta <R>. Please tell me what is the problem with my calculation.

How could one decide this F-sublattice displacement value(0.045102 Ã…)?

Any body would like to focus light on this topic.

thanks in advance,[/quote]

How could one decide this F-sublattice displacement value(0.045102 Ã…)?

I can answer this one--based on the diplacement of 0.01 (0.05n to 0.0510) in the lattice, and 4.5102 scaling factor (unit cell is 4.5102 A)
0.01 x 4.5102 = 0.045102 A. Why did they choose this one, and not another? Small disturbances are necessary, and they chose 0.01 as a representative (1% of unit cell) displacement.