VASP calculates the ion-clamped static dielectric tensor
(6.43) |
(6.44) |
(6.45) |
To this end VASP will perform essentially three successive calculations, with:
EFIELD_PEAD= 0 0,
EFIELD_PEAD= 0 0, and
EFIELD_PEAD= 0 0 .
By default, VASP uses
eV/Å.
This default can be overwritten by specifying (see Sec. 6.67.3):
The relevant output is found in the OUTCAR, immediately following
the lines (see Sec. 6.72.4 as well):
MACROSCOPIC STATIC DIELECTRIC TENSOR (including local field effects)
BORN EFFECTIVE CHARGES (including local field effects)
PIEZOELECTRIC TENSOR (including local field effects)
In the above, "including local field effects" pertains to the fact that
changes in the orbitals due to the electric field induce changes in the
Hartree- and exchange-correlation potential.
One may choose to limit this to changes in the Hartree potential alone,
by specifying:
LRPA=.TRUE. (Default: .FALSE.)
This is commonly referred to as the response within the
"Random Phase Approximation" (RPA), or the "neglect of local field effects".
The OUTCAR file will now contain additional sections, headed by the lines:
MACROSCOPIC STATIC DIELECTRIC TENSOR (excluding local field effects)
BORN EFFECTIVE CHARGES (excluding local field effects)
PIEZOELECTRIC TENSOR (excluding local field effects)
N.B.: For standard DFT functionals , , and may be more easily calculated from density functional perturbation theory (LEPSILON=.TRUE., see Sec. 6.72.4). For functionals that depend not only on the density but also explicitly on the orbitals, like hybrid functionals, density functional perturbation theory is presently not implemented and LEPSILON=.TRUE. is not applicable.