KERNEL TRUNCATION/FACTOR: Difference between revisions

Revision as of 11:25, 17 March 2026

Default: KERNEL_TRUNCATION/FACTOR	= $\sqrt{3}$	if `KERNEL_TRUNCATION/IDIMENSIONALITY = 0`
	= 1	if `KERNEL_TRUNCATION/IDIMENSIONALITY = 2`

Description: Determines the spatial extent of the truncated Coulomb interaction relative to the computational cell dimension along the truncation direction.

KERNEL_TRUNCATION/FACTOR defines the cutoff distance of the Coulomb-kernel-truncation boundary. It is expressed as a fraction of the simulation-cell length along the truncated axis (e.g., the surface normal for 2D systems ISURFACE).

Mind:

IfKERNEL_TRUNCATION/LTRUNCATE = F, KERNEL_TRUNCATION/FACTOR is ignored.
Available as of VASP.6.5.0.

References

@@ Line 1: / Line 1: @@
 {{TAGDEF|KERNEL_TRUNCATION/FACTOR| real}}
 {{DEF|KERNEL_TRUNCATION/FACTOR|$\sqrt{3}$|if {{TAG|KERNEL_TRUNCATION/IDIMENSIONALITY|0}}|1|if {{TAG|KERNEL_TRUNCATION/IDIMENSIONALITY|2}}}}
+{{DISPLAYTITLE:KERNEL_TRUNCATION/FACTOR}}
 '''Description:'''
-{{TAG|KERNEL_TRUNCATION/FACTOR}} determines the spatial extent of the truncated Coulomb interaction relative to the full cell dimension along the truncation direction{{cite|vijay:prb:2025}}.
+Determines the spatial extent of the truncated Coulomb interaction relative to the computational cell dimension along the truncation direction.
 ----
-This tag defines the cutoff distance of the Coulomb kernel truncation boundary. It is expressed as a fraction of the simulation cell length along the truncated axis (e.g., the surface normal for 2D systems).
+{{TAG|KERNEL_TRUNCATION/FACTOR}} defines the cutoff distance of the Coulomb-kernel-truncation boundary. It is expressed as a fraction of the simulation-cell length along the truncated axis (e.g., the surface normal for 2D systems {{TAG|ISURFACE}}).
 {{NB|mind|
-*{{TAG|KERNEL_TRUNCATION/LTRUNCATE}} must be set to <code>.TRUE.</code> for {{TAG|KERNEL_TRUNCATION/FACTOR}} to take effect.
+*If{{TAG|KERNEL_TRUNCATION/LTRUNCATE|F}}, {{TAG|KERNEL_TRUNCATION/FACTOR}} is ignored.
-*This tag is only available as of VASP.6.5.0.}}
+*Available as of VASP.6.5.0.}}
-{{NB|warning|When padding is used, the vaccum is added on the edges of the cell, as such it is very important that the motif is centered in the simulation box. If you encounter problems using Coulomb truncation with padding, try the same calculations without padding (see examples bellow).}}
-== Example ==
-<pre>
-KERNEL_TRUNCATION {
-     LTRUNCATE       = T
-     IDIMENSIONALITY = 2
-     ISURFACE        = 3
-     IPAD            = 2
-     FACTOR          = 1
-}
-</pre>
-In this case an additional empty cell is added along the z direciton as padding. The coulomb interaction is truncated beyond a z length. This ensures maximum usage of the simulation box.
-<pre>
-KERNEL_TRUNCATION {
-     LTRUNCATE       = T
-     IDIMENSIONALITY = 2
-     ISURFACE        = 3
-     IPAD            = 1
-     FACTOR          = 0.5
-}
-</pre>
-This setup corresponds to truncating the Coulomb interaction along the surface normal (z-direction) for a 2D material, using no vacuum padding and a truncation length of z/2. In this case, half of the simulation box is effectively unused, but the algorithm remains simpler. This configuration can be useful for debugging purposes.
 == Related tags and articles ==