KERNEL TRUNCATION/LTRUNCATE - Revision history

Svijay: /* Example */

2026-03-18T15:24:26Z

Example

← Older revision		Revision as of 15:24, 18 March 2026
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	This setup corresponds to truncating the Coulomb interaction along the surface normal direction (say, along z) 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 and will produce a potential that is not desired.		This setup corresponds to truncating the Coulomb interaction along the surface normal direction (say, along z) 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 and will produce a potential that is not desired.
	However, the algorithm is much simpler.		However, the algorithm is much simpler.
	We recommend this configuration ~~can~~ for debugging purposes.		We recommend this configuration for debugging purposes.

	== Related tags and articles ==		== Related tags and articles ==

Svijay: /* Example */

2026-03-18T15:24:07Z

Example

← Older revision		Revision as of 15:24, 18 March 2026
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	</pre>		</pre>

	This setup corresponds to truncating the Coulomb interaction along the surface normal 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 and will produce a potential that is not desired.		This setup corresponds to truncating the Coulomb interaction along the surface normal direction (say, along z) 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 and will produce a potential that is not desired.
	However, the algorithm is much simpler.		However, the algorithm is much simpler.
	We recommend this configuration can for debugging purposes.		We recommend this configuration can for debugging purposes.

Svijay: /* Example */

2026-03-18T15:23:47Z

Example

← Older revision		Revision as of 15:23, 18 March 2026
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	</pre>		</pre>
	In this case, we pad the cell along the surface normal direction.		In this case, we pad the cell along the surface normal direction.
	The Coulomb interaction is truncated beyond the boundaries of the cell along ~~the surface normal~~ direction.		The Coulomb interaction is truncated beyond the boundaries of the cell along this direction.
	<pre>		<pre>
	KERNEL_TRUNCATION {		KERNEL_TRUNCATION {

Svijay: /* Example */

2026-03-18T15:22:11Z

Example

← Older revision		Revision as of 15:22, 18 March 2026
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	In this case, we pad the cell along the surface normal direction.		In this case, we pad the cell along the surface normal direction.
	The Coulomb interaction is truncated beyond the boundaries of the cell along the surface normal direction.		The Coulomb interaction is truncated beyond the boundaries of the cell along the surface normal direction.


	<pre>		<pre>
	KERNEL_TRUNCATION {		KERNEL_TRUNCATION {

Svijay: /* Example */

2026-03-18T15:21:28Z

Example

← Older revision		Revision as of 15:21, 18 March 2026
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	IDIMENSIONALITY = 2		IDIMENSIONALITY = 2
	ISURFACE = 3		ISURFACE = 3
	~~IPAD~~ = 2		LCOARSEN = F
	~~FACTOR = 1~~
	}		}
	</pre>		</pre>
	In this case ~~an additional empty~~ cell ~~is added~~ along the z direction ~~as padding~~. The Coulomb interaction is truncated beyond ~~a z length. This ensures maximum usage~~ of the ~~simulation box~~.		In this case, we pad the cell along the surface normal direction.
			The Coulomb interaction is truncated beyond the boundaries of the cell along the surface normal direction.


	<pre>		<pre>
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	</pre>		</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.		This setup corresponds to truncating the Coulomb interaction along the surface normal 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 and will produce a potential that is not desired.
			However, the algorithm is much simpler.
			We recommend this configuration can for debugging purposes.

	== Related tags and articles ==		== Related tags and articles ==

Svijay: Typo

2026-03-18T15:15:00Z

Typo

← Older revision		Revision as of 15:15, 18 March 2026
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	}		}
	</pre>		</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.		In this case an additional empty cell is added along the z direction as padding. The Coulomb interaction is truncated beyond a z length. This ensures maximum usage of the simulation box.

	<pre>		<pre>

Huebsch at 13:06, 17 March 2026

2026-03-17T13:06:18Z

← Older revision		Revision as of 13:06, 17 March 2026
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	*This tag is only available as of VASP.6.5.0.}}		*This tag is only available as of VASP.6.5.0.}}
	Detailed information about the setting are documented on respective related tags.		Detailed information about the setting are documented on respective related tags.
	{{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).}}		{{NB\|warning\|When padding is used, the vaccum is added on the edges of the cell, therefore it is very important there are no atoms on the cell boundary in the non-periodic direction. We recommend centering the motif in the simulation box. If you encounter problems using Coulomb truncation with padding, try the same calculations without padding (see examples bellow).}}
	== Example ==		== Example ==

Huebsch at 11:21, 17 March 2026

2026-03-17T11:21:30Z

@@ Line 4: / Line 4: @@
 ----
 Setting {{TAG|KERNEL_TRUNCATION/LTRUNCATE}} = T  switches on the Coulomb-kernel-truncation method{{cite|vijay:prb:2025}}{{cite|rozzi:prb:2006}}{{cite|sohier:prb:2017}}. It effectively removes interactions with periodic replicas in non-periodic directions. In other words, the interactions are removed along the surface normal for [[2D materials]], and along all directions for 0D systems, i.e. for isolated atoms and molecules.
-{{NB|important| Slabs must be centered in the unit cell.}}
 In the simplest implementation of the Coulomb-kernel-truncation method ({{TAG|KERNEL_TRUNCATION/LCOARSEN|F}}), the computational cell provided in the {{FILE|POSCAR}} file is internally padded by an additional vacuum (see {{TAG|KERNEL_TRUNCATION/IPAD}}). This implies increasing the [[Energy cutoff and FFT meshes|FFT-grid sizes]] by a certain factor and thus leads to a significant increase in computational cost.
 {{NB|tip|Use the {{TAG|KERNEL_TRUNCATION/LCOARSEN|T}} to avoid the increased [[Energy cutoff and FFT meshes|FFT-grid sizes]].}}
@@ Line 11: / Line 11: @@
 *This tag is only available as of VASP.6.5.0.}}
 Detailed information about the setting are documented on respective related tags.
 == Related tags and articles ==

Huebsch at 10:57, 17 March 2026

2026-03-17T10:57:25Z

← Older revision		Revision as of 10:57, 17 March 2026
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	Setting {{TAG\|KERNEL_TRUNCATION/LTRUNCATE}} = T switches on the Coulomb-kernel-truncation method{{cite\|vijay:prb:2025}}{{cite\|rozzi:prb:2006}}{{cite\|sohier:prb:2017}}. It effectively removes interactions with periodic replicas in non-periodic directions. In other words, the interactions are removed along the surface normal for [[2D materials]], and along all directions for 0D systems, i.e. for isolated atoms and molecules.		Setting {{TAG\|KERNEL_TRUNCATION/LTRUNCATE}} = T switches on the Coulomb-kernel-truncation method{{cite\|vijay:prb:2025}}{{cite\|rozzi:prb:2006}}{{cite\|sohier:prb:2017}}. It effectively removes interactions with periodic replicas in non-periodic directions. In other words, the interactions are removed along the surface normal for [[2D materials]], and along all directions for 0D systems, i.e. for isolated atoms and molecules.
	{{NB\|important\| Slabs must be centered in the unit cell.}}		{{NB\|important\| Slabs must be centered in the unit cell.}}
	In the simplest implementation of the Coulomb-kernel-truncation method ({{TAG\|KERNEL_TRUNCATION/LCOARSEN\|F}}), the computational cell provided in the {{FILE\|POSCAR}} file is internally padded by an additional vacuum ~~that is of the same extend as the computational cell in each direction~~. This implies increasing the [[Energy cutoff and FFT meshes\|FFT-grid sizes]] by a certain factor ~~(see {{TAG\|KERNEL_TRUNCATION/IPAD}})~~ and thus leads to a significant increase in computational cost.		In the simplest implementation of the Coulomb-kernel-truncation method ({{TAG\|KERNEL_TRUNCATION/LCOARSEN\|F}}), the computational cell provided in the {{FILE\|POSCAR}} file is internally padded by an additional vacuum (see {{TAG\|KERNEL_TRUNCATION/IPAD}}). This implies increasing the [[Energy cutoff and FFT meshes\|FFT-grid sizes]] by a certain factor and thus leads to a significant increase in computational cost.
	{{NB\|tip\|Use the {{TAG\|KERNEL_TRUNCATION/LCOARSEN\|T}} to avoid the increased [[Energy cutoff and FFT meshes\|FFT-grid sizes]].}}		{{NB\|tip\|Use the {{TAG\|KERNEL_TRUNCATION/LCOARSEN\|T}} to avoid the increased [[Energy cutoff and FFT meshes\|FFT-grid sizes]].}}
	{{NB\|mind\|		{{NB\|mind\|

Huebsch at 10:55, 17 March 2026

2026-03-17T10:55:45Z

← Older revision		Revision as of 10:55, 17 March 2026
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	Description: Truncates the Coulomb kernel to remove [[:Category:electrostatics\|electrostatic interactions]] along non-periodic dimensions.		Description: Truncates the Coulomb kernel to remove [[:Category:electrostatics\|electrostatic interactions]] along non-periodic dimensions.
	----		----
	Setting {{TAG\|KERNEL_TRUNCATION/LTRUNCATE}} = T switches on the Coulomb-kernel-truncation method{{cite\|vijay:prb:2025}}. It effectively removes interactions with periodic replicas in non-periodic directions. In other words, the interactions are removed along the surface normal for [[2D materials]], and along all directions for 0D systems, i.e. for isolated atoms and molecules.		Setting {{TAG\|KERNEL_TRUNCATION/LTRUNCATE}} = T switches on the Coulomb-kernel-truncation method{{cite\|vijay:prb:2025}}{{cite\|rozzi:prb:2006}}{{cite\|sohier:prb:2017}}. It effectively removes interactions with periodic replicas in non-periodic directions. In other words, the interactions are removed along the surface normal for [[2D materials]], and along all directions for 0D systems, i.e. for isolated atoms and molecules.
	{{NB\|important\| Slabs must be centered in the unit cell.}}		{{NB\|important\| Slabs must be centered in the unit cell.}}
	In the simplest implementation of the Coulomb-kernel-truncation method ({{TAG\|KERNEL_TRUNCATION/LCOARSEN\|F}}), the computational cell provided in the {{FILE\|POSCAR}} file is internally padded by an additional vacuum that is of the same extend as the computational cell in each direction. This implies increasing the [[Energy cutoff and FFT meshes\|FFT-grid sizes]] by a certain factor (see {{TAG\|KERNEL_TRUNCATION/IPAD}}) and thus leads to a significant increase in computational cost.		In the simplest implementation of the Coulomb-kernel-truncation method ({{TAG\|KERNEL_TRUNCATION/LCOARSEN\|F}}), the computational cell provided in the {{FILE\|POSCAR}} file is internally padded by an additional vacuum that is of the same extend as the computational cell in each direction. This implies increasing the [[Energy cutoff and FFT meshes\|FFT-grid sizes]] by a certain factor (see {{TAG\|KERNEL_TRUNCATION/IPAD}}) and thus leads to a significant increase in computational cost.