LPHON POLAR

LPHON_POLAR = .TRUE. | .FALSE.
Default: LPHON_POLAR = .FALSE. 

Description: LPHON_POLAR includes dipole-dipole corrections in the computation of the phonon dispersion. For this mode, PHON_DIELECTRIC and PHON_BORN_CHARGES must also be set.

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If the material is non-metallic and polar (i.e. two or more atoms in the unit cell carry nonzero Born effective charge tensors), a special treatment of the long-range dipole-dipole interaction is required to obtain a smooth phonon dispersion. This is activated by setting LPHON_POLAR=.TRUE. and supplying the static dielectric tensor (PHON_DIELECTRIC) and the Born-effective charges (PHON_BORN_CHARGES) which can be obtained in a separate VASP calculation using the LEPSILON or LCALCEPS tag. The dipole-dipole part of the interatomic force-constants is evaluated using an Ewald summation with the number of $\mathbf{G}$ vectors determined by the cutoff length (PHON_G_CUTOFF).

In the case of metals, the dielectric function is infinite, for nonpolar semiconductors the Born effective charges are zero which in both cases means that the long-range interatomic force-constants are zero and this dipole-dipole correction does not need to be applied.

Mind: Only available as of VASP 6.3.2.

Related tags and articles

QPOINTS, LPHON_DISPERSION, PHON_NWRITE, PHON_DIELECTRIC, PHON_BORN_CHARGES, PHON_G_CUTOFF

Examples that use this tag