PHON G CUTOFF: Difference between revisions

Latest revision as of 10:36, 23 October 2023

Default: PHON_G_CUTOFF

= 8.0

Description: PHON_G_CUTOFF sets the cutoff radius in reciprocal space used to determine the number of $\mathbf{G}$ vectors involved in the Ewald sum in polar phonon calculations.

The Ewald sum that accounts for the long-range electrostatic interactions in phonon calculations runs over all G-vectors inside a cutoff sphere. The radius of this sphere is given by PHON_G_CUTOFF as a multiple of the longest reciprocal lattice vector of the primitive cell (as detected by VASP). Specifying the cutoff this way (as opposed to an absolute length or energy) ensures a default value that is relatively system-independent.

The default value of PHON_G_CUTOFF is a safe choice in most cases. Lowering PHON_G_CUTOFF can result in faster phonon calculations. However, ensure that the phonon spectrum is properly converged. If you run into convergence problems, try raising the value until the phonon dispersion converges.

For more information on polar phonon calculations, see LPHON_POLAR.

Mind: Only available as of VASP 6.3.2.

@@ Line 1: / Line 1: @@
 {{DISPLAYTITLE:PHON_G_CUTOFF}}
 {{TAGDEF|PHON_G_CUTOFF| [real] }}
-{{DEF|PHON_G_CUTOFF|None|}}
+{{DEF|PHON_G_CUTOFF|8.0|}}
 Description: {{TAG|PHON_G_CUTOFF}} sets the cutoff radius in reciprocal space used to determine the number of <math>\mathbf{G}</math> vectors involved in the Ewald sum in polar phonon calculations.
 ----
-If the material is polar (i.e. has more than one atom type), a special treatment of the long-range dipole-dipole interaction is required to obtain a smooth phonon dispersion.
+The Ewald sum that accounts for the long-range electrostatic interactions in phonon calculations runs over all G-vectors inside a cutoff sphere.
-This is activated by setting {{TAG|LPHON_POLAR}}=.TRUE. and supplying the static dielectric tensor ({{TAG|PHON_DIELECTRIC}}) and the Born-effective charges ({{TAG|PHON_BORN_CHARGES}}) which can be obtained in a separate VASP calculation using the {{TAG|LEPSILON}} or {{TAG|LCALCEPS}} tag. The long-range part is evaluated using an Ewald sum with the number of <math>\mathbf{G}</math> vectors in reciprocal space being determined using a cutoff length ({{TAG|PHON_G_CUTOFF}}).
+The radius of this sphere is given by {{TAG|PHON_G_CUTOFF}} as a multiple of the longest reciprocal lattice vector of the primitive cell (as detected by VASP).
+Specifying the cutoff this way (as opposed to an absolute length or energy) ensures a default value that is relatively system-independent.
+The default value of {{TAG|PHON_G_CUTOFF}} is a safe choice in most cases.
+Lowering {{TAG|PHON_G_CUTOFF}} can result in faster phonon calculations.
+However, ensure that the phonon spectrum is properly converged.
+If you run into convergence problems, try raising the value until the phonon dispersion converges.
+For more information on polar phonon calculations, see {{TAG|LPHON_POLAR}}.
 {{NB|mind| Only available as of VASP 6.3.2.}}

Latest revision as of 10:36, 23 October 2023

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