LCALCPOL

LCALCPOL = .TRUE. | .FALSE.
Default: LCALCPOL = .FALSE. 

Description: LCALCPOL=.TRUE. switches on the evaluation of the Berry phase expressions for the macroscopic electronic polarization in accordance with the so-called Modern Theory of Polarization.

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For LCALCPOL=.TRUE., VASP calculates the electronic contribution to the polarization, along the three reciprocal lattice vectors G_i, i=1,2,3, (i.e. Σ_i P·G_i) in a single run (unlike LBERRY=.TRUE.).

An example: The fluorine displacement dipole (Born effective charge) in NaF.

• With INCAR file:

PREC = Med
EDIFF= 1E-6

ISMEAR = 0
DIPOL  = 0.25 0.25 0.25

LCALCPOL = .TRUE.

• KPOINTS file:

6x6x6
 0
Gamma
 6 6 6
 0 0 0

• POSCAR file:

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  0.5000000000000000

• and LDA Na_sv and F PAW datasets.

The OUTCAR file should now contain the following lines:

            Ionic dipole moment: p[ion]=(     2.25510     2.25510     2.25510 ) electrons Angst

 Total electronic dipole moment: p[elc]=(     0.00000     0.00000     0.00000 ) electrons Angst

To calculate the change in the electronic polarization of NaF due to the displacement of the fluorine sublattice we repeat the previous calculation with the following POSCAR file:

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  0.4900000000000000

The OUTCAR should now contain something very similar to the following lines:

            Ionic dipole moment: p[ion]=(     2.25510     2.25510     1.93939 ) electrons Angst

 Total electronic dipole moment: p[elc]=(     0.00000     0.00000     0.36061 ) electrons Angst

From the above one easily recognizes that the change in the electronic dipole moment due to the F-sublattice displacement is:

$\Delta\mathrm{p[elc]}=0.3606\hat{z}\;e\AA$

and the corresponding change in the ionic dipole moment:

$\Delta\mathrm{p[ion]}=1.93939-2.25510=-0.31571\hat{z}\;e\AA$

Thus the total change is found to be:

$\Delta\mathrm{p[tot]}=0.36061-0.31571=0.0449\hat{z}\;e\AA$

and considering that the F-sublattice was displaced by 0.045102 Å these calculations yield a Born effective charge for fluorine of Z^*=0.0449/0.045102= -0.995.

Related Tags and Sections

LCALCEPS, EFIELD_PEAD, LPEAD, IPEAD, LBERRY, IGPAR, NPPSTR, DIPOL, Berry phases and finite electric fields

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