Energy cutoff and FFT meshes - Revision history

Liebetreu: Reverted edit by Liebetreu (talk) to last revision by Ftran

2026-04-15T12:27:48Z

Reverted edit by Liebetreu (talk) to last revision by Ftran

← Older revision		Revision as of 12:27, 15 April 2026
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	The [[Projector-augmented-wave_formalism\|plane-wave expansion of the Kohn-Sham (KS) orbitals]] are associated to a mesh to perform FFTs from real space coordinates ~~<math>~~\mathbf{r}~~</math>~~ to reciprocal coordinates ~~<math>~~\mathbf{G}~~</math>~~ and vice versa. These have a very large impact on the accuracy of any ab-initio calculation particularly including basic [[Setting up an electronic minimization\|electronic minimization calculations]].		The [[Projector-augmented-wave_formalism\|plane-wave expansion of the Kohn-Sham (KS) orbitals]] are associated to a mesh to perform FFTs from real space coordinates $\mathbf{r}$ to reciprocal coordinates $\mathbf{G}$ and vice versa. These have a very large impact on the accuracy of any ab-initio calculation particularly including basic [[Setting up an electronic minimization\|electronic minimization calculations]].
	The so-called FFT mesh and thus basis-set truncation is a result of the selected energy cutoff ({{TAG\|ENCUT}}). It is one of the most important parameters for the accuracy. Some indications and illustrations on how to choose {{TAG\|ENCUT}} or other related tags like {{TAG\|PREC}} are provided below.		The so-called FFT mesh and thus basis-set truncation is a result of the selected energy cutoff ({{TAG\|ENCUT}}). It is one of the most important parameters for the accuracy. Some indications and illustrations on how to choose {{TAG\|ENCUT}} or other related tags like {{TAG\|PREC}} are provided below.

Liebetreu at 14:17, 14 April 2026

2026-04-14T14:17:16Z

← Older revision		Revision as of 14:17, 14 April 2026
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	The [[Projector-augmented-wave_formalism\|plane-wave expansion of the Kohn-Sham (KS) orbitals]] are associated to a mesh to perform FFTs from real space coordinates $\mathbf{r}$ to reciprocal coordinates $\mathbf{G}$ and vice versa. These have a very large impact on the accuracy of any ab-initio calculation particularly including basic [[Setting up an electronic minimization\|electronic minimization calculations]].		The [[Projector-augmented-wave_formalism\|plane-wave expansion of the Kohn-Sham (KS) orbitals]] are associated to a mesh to perform FFTs from real space coordinates <math>\mathbf{r}</math> to reciprocal coordinates <math>\mathbf{G}</math> and vice versa. These have a very large impact on the accuracy of any ab-initio calculation particularly including basic [[Setting up an electronic minimization\|electronic minimization calculations]].
	The so-called FFT mesh and thus basis-set truncation is a result of the selected energy cutoff ({{TAG\|ENCUT}}). It is one of the most important parameters for the accuracy. Some indications and illustrations on how to choose {{TAG\|ENCUT}} or other related tags like {{TAG\|PREC}} are provided below.		The so-called FFT mesh and thus basis-set truncation is a result of the selected energy cutoff ({{TAG\|ENCUT}}). It is one of the most important parameters for the accuracy. Some indications and illustrations on how to choose {{TAG\|ENCUT}} or other related tags like {{TAG\|PREC}} are provided below.

Ftran at 09:25, 24 October 2025

2025-10-24T09:25:03Z

← Older revision		Revision as of 09:25, 24 October 2025
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	The [[Projector-augmented-wave_formalism\|plane-wave expansion of the Kohn-Sham (KS) orbitals]] are associated to a mesh to perform FFTs from real space coordinates $\mathbf{r}$ to reciprocal coordinates $\mathbf{G}$ and ~~vize~~ versa. These have a very large impact on the accuracy of any ab-initio calculation particularly including basic [[Setting up an electronic minimization\|electronic minimization calculations]].		The [[Projector-augmented-wave_formalism\|plane-wave expansion of the Kohn-Sham (KS) orbitals]] are associated to a mesh to perform FFTs from real space coordinates $\mathbf{r}$ to reciprocal coordinates $\mathbf{G}$ and vice versa. These have a very large impact on the accuracy of any ab-initio calculation particularly including basic [[Setting up an electronic minimization\|electronic minimization calculations]].
	The so-called FFT mesh and thus basis-set truncation is a result of the selected energy cutoff ({{TAG\|ENCUT}}). It is one of the most important parameters for the accuracy. Some indications and illustrations on how to choose {{TAG\|ENCUT}} or other related tags like {{TAG\|PREC}} are provided below.		The so-called FFT mesh and thus basis-set truncation is a result of the selected energy cutoff ({{TAG\|ENCUT}}). It is one of the most important parameters for the accuracy. Some indications and illustrations on how to choose {{TAG\|ENCUT}} or other related tags like {{TAG\|PREC}} are provided below.

Huebsch: Huebsch moved page Energy cut off and FFT mesh to Energy cutoff and FFT meshes

2025-10-24T08:54:47Z

Huebsch moved page Energy cut off and FFT mesh to Energy cutoff and FFT meshes

← Older revision		Revision as of 08:54, 24 October 2025
(No difference)

Huebsch at 08:54, 24 October 2025

2025-10-24T08:54:04Z

Show changes

Ftran at 14:44, 16 October 2025

2025-10-16T14:44:23Z

← Older revision		Revision as of 14:44, 16 October 2025
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	They are determined by the energy cutoff {{TAG\|ENCUT}}, which is one of the most important parameters		They are determined by the energy cutoff {{TAG\|ENCUT}}, which is one of the most important parameters
	for the accuracy. {{TAG\|ENCUT}} needs to be chosen large enough to ensure that the errors due to the basis-set		for the accuracy. {{TAG\|ENCUT}} needs to be chosen large enough to ensure that the errors due to the basis-set
	truncation and finite mesh size are below the required accuracy. Some indications on how to choose {{TAG\|ENCUT}}		truncation and finite mesh size are below the required accuracy. Some indications and illustrations on how to choose {{TAG\|ENCUT}}
	or other related tags like {{TAG\|PREC}} are provided below.		or other related tags like {{TAG\|PREC}} are provided below.

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	When {{TAG\|ADDGRID}}=.TRUE., an additional 'support' grid is used for the evaluation of the augmentation charges.		When {{TAG\|ADDGRID}}=.TRUE., an additional 'support' grid is used for the evaluation of the augmentation charges.
	This grid has a size of <math>2\times</math>({{TAG\|NGXF}},{{TAG\|NGYF}},{{TAG\|NGZF}}), i.e., it has twice more points that the 'fine' grid along each lattice vector. The support grid often helps to reduce the noise in the forces, however as explained in more detail at {{TAG\|ADDGRID}} it should be used with caution.		This grid has a size of <math>2\times</math>({{TAG\|NGXF}},{{TAG\|NGYF}},{{TAG\|NGZF}}), i.e., it has twice more points that the 'fine' grid along each lattice vector. The support grid often helps to reduce the noise in the forces, however as explained in more detail at {{TAG\|ADDGRID}} it should be used with caution.

			= Examples =

			== Volume relaxation and pressure ==

			An illustration of the effect of the energy cutoff {{TAG\|ENCUT}} on the results is given for the [[Volume_relaxation\|equilibrium volume]] and [[Pulay_stress\|pressure]] of diamond. It clearly shows the noise induced by using an unconverged value for {{TAG\|ENCUT}}.

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

Ftran at 12:50, 16 October 2025

2025-10-16T12:50:26Z

← Older revision		Revision as of 12:50, 16 October 2025
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	The ~~basis set~~ and ~~FFT~~ mesh have a very large impact on the accuracy of a calculation.		The [[Projector-augmented-wave_formalism\|plane-wave expansion of the orbitals]] and the associated mesh to perform the FFTs have a very large impact on the accuracy of a calculation.
	They are determined by the energy cutoff {{TAG\|ENCUT}}, which is one of the most important parameters		They are determined by the energy cutoff {{TAG\|ENCUT}}, which is one of the most important parameters
	for the accuracy. {{TAG\|ENCUT}} needs to be chosen large enough to ensure that the errors due to the basis-set		for the accuracy. {{TAG\|ENCUT}} needs to be chosen large enough to ensure that the errors due to the basis-set
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	The energy cutoff {{TAG\|ENCUT}} should be chosen according to the pseudopotential ({{TAG\|POTCAR}})		The energy cutoff {{TAG\|ENCUT}} should be chosen according to the pseudopotential ({{TAG\|POTCAR}})
	and required accuracy. The default value for {{TAG\|ENCUT}} is the largest among the ENMAX values found		and required accuracy. The default value for {{TAG\|ENCUT}} is the largest among the ENMAX values found
	in the {{TAG\|POTCAR}} file. ~~This is~~ the ~~minimum value that~~ should be used, since ~~smaller values~~		in the {{TAG\|POTCAR}} file. Values smaller than the default should never be used, since
	may possibly lead to large errors ~~and must not be used~~. This default minimal value		they may possibly lead to large errors. This default minimal value
	should usually result in an error in the cohesive energy which is less than 10 meV.		should usually result in an error in the cohesive energy which is less than 10 meV.
	{{NB\|mind\|The recommended and usual procedure for choosing {{TAG\|ENCUT}} is to perform a series of calculations with different {{TAG\|ENCUT}} values (larger than the default one) and to monitor the results for the property of interest.}}		{{NB\|mind\|The recommended and usual procedure for choosing {{TAG\|ENCUT}} is to perform a series of calculations with different {{TAG\|ENCUT}} values (larger than the default one) and to monitor the results for the property of interest.}}
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	----		----
	[[Category:Howto]][[Category:Calculation_setup]]		<!--[[Category:Howto]][[Category:Calculation_setup]]-->

Ftran at 12:25, 16 October 2025

2025-10-16T12:25:44Z

Show changes

Ftran at 13:37, 13 October 2025

2025-10-13T13:37:50Z

← Older revision		Revision as of 13:37, 13 October 2025
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	setting. This can be done either by hand (setting {{TAG\|NGXF}}		setting. This can be done either by hand (setting {{TAG\|NGXF}}
	in the param.inc file) or by giving a		in the param.inc file) or by giving a
	value for {{TAG\|ENAUG}} in the {{TAG\|INCAR} file.		value for {{TAG\|ENAUG}} in the {{TAG\|INCAR}} file.

	As for the soft part of the charge density the		As for the soft part of the charge density the

Ftran at 12:06, 13 October 2025

2025-10-13T12:06:45Z

← Older revision		Revision as of 12:06, 13 October 2025
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	:<math>		:<math>
	\~~bold~~{G} = 2 \pi m_x \~~bold~~{g}^{(x)} ,\quad \~~bold~~{G} = 2 \pi m_y \~~bold~~{g}^{(y)} ,\quad		\mathbf{G} = 2 \pi m_x \mathbf{g}^{(x)} ,\quad \mathbf{G} = 2 \pi m_y \mathbf{g}^{(y)} ,\quad
	\~~bold~~{G} = 2 \pi m_z \~~bold~~{g}^{(z)}.		\mathbf{G} = 2 \pi m_z \mathbf{g}^{(z)}.
	</math>		</math>

← Older revision		Revision as of 14:44, 16 October 2025
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	They are determined by the energy cutoff {{TAG\|ENCUT}}, which is one of the most important parameters		They are determined by the energy cutoff {{TAG\|ENCUT}}, which is one of the most important parameters
	for the accuracy. {{TAG\|ENCUT}} needs to be chosen large enough to ensure that the errors due to the basis-set		for the accuracy. {{TAG\|ENCUT}} needs to be chosen large enough to ensure that the errors due to the basis-set
	truncation and finite mesh size are below the required accuracy. Some indications on how to choose {{TAG\|ENCUT}}		truncation and finite mesh size are below the required accuracy. Some indications and illustrations on how to choose {{TAG\|ENCUT}}
	or other related tags like {{TAG\|PREC}} are provided below.		or other related tags like {{TAG\|PREC}} are provided below.

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	When {{TAG\|ADDGRID}}=.TRUE., an additional 'support' grid is used for the evaluation of the augmentation charges.		When {{TAG\|ADDGRID}}=.TRUE., an additional 'support' grid is used for the evaluation of the augmentation charges.
	This grid has a size of <math>2\times</math>({{TAG\|NGXF}},{{TAG\|NGYF}},{{TAG\|NGZF}}), i.e., it has twice more points that the 'fine' grid along each lattice vector. The support grid often helps to reduce the noise in the forces, however as explained in more detail at {{TAG\|ADDGRID}} it should be used with caution.		This grid has a size of <math>2\times</math>({{TAG\|NGXF}},{{TAG\|NGYF}},{{TAG\|NGZF}}), i.e., it has twice more points that the 'fine' grid along each lattice vector. The support grid often helps to reduce the noise in the forces, however as explained in more detail at {{TAG\|ADDGRID}} it should be used with caution.

			= Examples =

			== Volume relaxation and pressure ==

			An illustration of the effect of the energy cutoff {{TAG\|ENCUT}} on the results is given for the [[Volume_relaxation\|equilibrium volume]] and [[Pulay_stress\|pressure]] of diamond. It clearly shows the noise induced by using an unconverged value for {{TAG\|ENCUT}}.

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