Technical errors - Revision history

Miranda.henrique at 16:36, 23 November 2021

2021-11-23T16:36:00Z

← Older revision		Revision as of 16:36, 23 November 2021
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	*Errors due to the cut-off {{TAG\|ENCUT}}. This error is highly transferable, i.e. the default cutoff {{TAG\|ENCUT}} (read from the {{TAG\|POTCAR}} file) is in most cases safe, and one can expect that energy differences will be accurate within a few meV (see {{TAG\|Energy cut off and FFT mesh}}). An exception is the stress tensor which converges notoriously slow with respect to the size of the plane wave basis set (see {{TAG\|Energy vs volume Volume relaxations and Pulay stress}}).		*Errors due to the cut-off {{TAG\|ENCUT}}. This error is highly transferable, i.e. the default cutoff {{TAG\|ENCUT}} (read from the {{TAG\|POTCAR}} file) is in most cases safe, and one can expect that energy differences will be accurate within a few meV (see {{TAG\|Energy cut off and FFT mesh}}). An exception is the stress tensor which converges notoriously slow with respect to the size of the plane wave basis set (see {{TAG\|Energy vs volume Volume relaxations and Pulay stress}}).
	*Wrap around errors (see {{TAG\|Wrap-around errors}}): These errors are due to an insufficient FFT mesh and they are not as well behaved as the errors due to the energy cut off (see {{TAG\|Energy cut off and FFT mesh}}). But once again, if one uses the default cut off (read from the {{TAG\|POTCAR}} file) the wrap around errors are usually very small (a few meV per atom) even if the FFT mesh is not sufficient. The reason is that the default cut offs in VASP are rather large, and therefore the charge density and the potentials contain only small components in the region where the wrap around error occurs.		*Wrap around errors (see {{TAG\|Wrap-around errors}}): These errors are due to an insufficient FFT mesh and they are not as well behaved as the errors due to the energy cut off (see {{TAG\|Energy cut off and FFT mesh}}). But once again, if one uses the default cut off (read from the {{TAG\|POTCAR}} file) the wrap around errors are usually very small (a few meV per atom) even if the FFT mesh is not sufficient. The reason is that the default cut offs in VASP are rather large, and therefore the charge density and the potentials contain only small components in the region where the wrap around error occurs.
	*Errors due to the real space projection: Real space projection always introduces additional (small) errors. These errors are also quite well behaved i.e. if one uses the same real space projection operators all the time, the errors are almost constants. Anyway, one should try to avoid the evaluation of energy differences between calculations with {{TAG\|LREAL}}=''.FALSE.'' and {{TAG\|LREAL}}=''.TRUE.'' (see {{TAG\|LREAL}}). Mind that for {{TAG\|LREAL}}=''~~.TRUE.~~'' (the recommended setting) the real space operators are optimized by VASP according to {{TAG\|ENCUT}} and {{TAG\|PREC~~}} and {{TAG\|ROPT~~}} i.e. one gets different real space projection operators if {{TAG\|ENCUT}} or {{TAG\|PREC}} is changed.		*Errors due to the real space projection: Real space projection always introduces additional (small) errors. These errors are also quite well behaved i.e. if one uses the same real space projection operators all the time, the errors are almost constants. Anyway, one should try to avoid the evaluation of energy differences between calculations with {{TAG\|LREAL}}=''.FALSE.'' and {{TAG\|LREAL}}=''.TRUE.'' (see {{TAG\|LREAL}}). Mind that for {{TAG\|LREAL}}=''Auto'' (the recommended setting) the real space operators are optimized by VASP according to {{TAG\|ENCUT}} and {{TAG\|PREC}} i.e. one gets different real space projection operators if {{TAG\|ENCUT}} or {{TAG\|PREC}} is changed.

	In conclusion, to minimize errors one should use the same setting for {{TAG\|ENCUT}}, {{TAG\|ENAUG}}, {{TAG\|PREC}}, {{TAG\|LREAL}} and {{TAG\|ROPT}} throughout all calculations, and these flags should be specified explicitly in the {{TAG\|INCAR}} file. In addition it is also preferable to use the same supercell for all calculations whenever possible.		In conclusion, to minimize errors one should use the same setting for {{TAG\|ENCUT}}, {{TAG\|ENAUG}}, {{TAG\|PREC}}, {{TAG\|LREAL}} and {{TAG\|ROPT}} throughout all calculations, and these flags should be specified explicitly in the {{TAG\|INCAR}} file. In addition it is also preferable to use the same supercell for all calculations whenever possible.

Vaspmaster at 11:42, 3 November 2020

2020-11-03T11:42:07Z

← Older revision		Revision as of 11:42, 3 November 2020
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	[[Category:~~Calculational issues~~]]		[[Category:Common Pitfalls]]

Karsai at 08:52, 29 March 2019

2019-03-29T08:52:44Z

← Older revision		Revision as of 08:52, 29 March 2019
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	Technical errors fall into four categories:		Technical errors fall into four categories:
	*Errors due to k-point sampling. This will be discussed in {{TAG\|k~~-point~~ smearing}}. Mind that the errors due to the k-point mesh are not transferable i.e. a <math> 9\times 9\times 9</math> k-points grid leads to a completely different error for fcc, bcc and sc. It is therefore absolutely essential to be very careful with respect to the k-point sampling.		*Errors due to k-point sampling. This will be discussed in {{TAG\|Number of k points and method for smearing}}. Mind that the errors due to the k-point mesh are not transferable i.e. a <math> 9\times 9\times 9</math> k-points grid leads to a completely different error for fcc, bcc and sc. It is therefore absolutely essential to be very careful with respect to the k-point sampling.
	*Errors due to the cut-off {{TAG\|ENCUT}}. This error is highly transferable, i.e. the default cutoff {{TAG\|ENCUT}} (read from the {{TAG\|POTCAR}} file) is in most cases safe, and one can expect that energy differences will be accurate within a few meV (see {{TAG\|Energy cut off and FFT mesh}}). An exception is the stress tensor which converges notoriously slow with respect to the size of the plane wave basis set (see {{TAG\|Energy vs volume Volume relaxations and Pulay stress}}).		*Errors due to the cut-off {{TAG\|ENCUT}}. This error is highly transferable, i.e. the default cutoff {{TAG\|ENCUT}} (read from the {{TAG\|POTCAR}} file) is in most cases safe, and one can expect that energy differences will be accurate within a few meV (see {{TAG\|Energy cut off and FFT mesh}}). An exception is the stress tensor which converges notoriously slow with respect to the size of the plane wave basis set (see {{TAG\|Energy vs volume Volume relaxations and Pulay stress}}).
	*Wrap around errors (see {{TAG\|Wrap-around errors}}): These errors are due to an insufficient FFT mesh and they are not as well behaved as the errors due to the energy cut off (see {{TAG\|Energy cut off and FFT mesh}}). But once again, if one uses the default cut off (read from the {{TAG\|POTCAR}} file) the wrap around errors are usually very small (a few meV per atom) even if the FFT mesh is not sufficient. The reason is that the default cut offs in VASP are rather large, and therefore the charge density and the potentials contain only small components in the region where the wrap around error occurs.		*Wrap around errors (see {{TAG\|Wrap-around errors}}): These errors are due to an insufficient FFT mesh and they are not as well behaved as the errors due to the energy cut off (see {{TAG\|Energy cut off and FFT mesh}}). But once again, if one uses the default cut off (read from the {{TAG\|POTCAR}} file) the wrap around errors are usually very small (a few meV per atom) even if the FFT mesh is not sufficient. The reason is that the default cut offs in VASP are rather large, and therefore the charge density and the potentials contain only small components in the region where the wrap around error occurs.

Karsai at 08:51, 29 March 2019

2019-03-29T08:51:50Z

← Older revision		Revision as of 08:51, 29 March 2019
Line 3:		Line 3:
	*Errors due to the cut-off {{TAG\|ENCUT}}. This error is highly transferable, i.e. the default cutoff {{TAG\|ENCUT}} (read from the {{TAG\|POTCAR}} file) is in most cases safe, and one can expect that energy differences will be accurate within a few meV (see {{TAG\|Energy cut off and FFT mesh}}). An exception is the stress tensor which converges notoriously slow with respect to the size of the plane wave basis set (see {{TAG\|Energy vs volume Volume relaxations and Pulay stress}}).		*Errors due to the cut-off {{TAG\|ENCUT}}. This error is highly transferable, i.e. the default cutoff {{TAG\|ENCUT}} (read from the {{TAG\|POTCAR}} file) is in most cases safe, and one can expect that energy differences will be accurate within a few meV (see {{TAG\|Energy cut off and FFT mesh}}). An exception is the stress tensor which converges notoriously slow with respect to the size of the plane wave basis set (see {{TAG\|Energy vs volume Volume relaxations and Pulay stress}}).
	*Wrap around errors (see {{TAG\|Wrap-around errors}}): These errors are due to an insufficient FFT mesh and they are not as well behaved as the errors due to the energy cut off (see {{TAG\|Energy cut off and FFT mesh}}). But once again, if one uses the default cut off (read from the {{TAG\|POTCAR}} file) the wrap around errors are usually very small (a few meV per atom) even if the FFT mesh is not sufficient. The reason is that the default cut offs in VASP are rather large, and therefore the charge density and the potentials contain only small components in the region where the wrap around error occurs.		*Wrap around errors (see {{TAG\|Wrap-around errors}}): These errors are due to an insufficient FFT mesh and they are not as well behaved as the errors due to the energy cut off (see {{TAG\|Energy cut off and FFT mesh}}). But once again, if one uses the default cut off (read from the {{TAG\|POTCAR}} file) the wrap around errors are usually very small (a few meV per atom) even if the FFT mesh is not sufficient. The reason is that the default cut offs in VASP are rather large, and therefore the charge density and the potentials contain only small components in the region where the wrap around error occurs.
	*Errors due to the real space projection: Real space projection always introduces additional (small) errors. These errors are also quite well behaved i.e. if one uses the same real space projection operators all the time, the errors are almost constants. Anyway, one should try to avoid the evaluation of energy differences between calculations with {{TAG\|LREAL}}=''.FALSE.'' and {{TAG\|LREAL}}=''.TRUE.'' (see {{TAG\|LREAL}}). Mind that for {{~~ŦAG~~\|LREAL}}=''.TRUE.'' (the recommended setting) the real space operators are optimized by VASP according to {{TAG\|ENCUT}} and {{TAG\|PREC}} and {{TAG\|ROPT}} i.e. one gets different real space projection operators if {{TAG\|ENCUT}} or {{TAG\|PREC}} is changed.		*Errors due to the real space projection: Real space projection always introduces additional (small) errors. These errors are also quite well behaved i.e. if one uses the same real space projection operators all the time, the errors are almost constants. Anyway, one should try to avoid the evaluation of energy differences between calculations with {{TAG\|LREAL}}=''.FALSE.'' and {{TAG\|LREAL}}=''.TRUE.'' (see {{TAG\|LREAL}}). Mind that for {{TAG\|LREAL}}=''.TRUE.'' (the recommended setting) the real space operators are optimized by VASP according to {{TAG\|ENCUT}} and {{TAG\|PREC}} and {{TAG\|ROPT}} i.e. one gets different real space projection operators if {{TAG\|ENCUT}} or {{TAG\|PREC}} is changed.

	In conclusion, to minimize errors one should use the same setting for {{TAG\|ENCUT}}, {{TAG\|ENAUG}}, {{TAG\|PREC}}, {{TAG\|LREAL}} and {{TAG\|ROPT}} throughout all calculations, and these flags should be specified explicitly in the {{TAG\|INCAR}} file. In addition it is also preferable to use the same supercell for all calculations whenever possible.		In conclusion, to minimize errors one should use the same setting for {{TAG\|ENCUT}}, {{TAG\|ENAUG}}, {{TAG\|PREC}}, {{TAG\|LREAL}} and {{TAG\|ROPT}} throughout all calculations, and these flags should be specified explicitly in the {{TAG\|INCAR}} file. In addition it is also preferable to use the same supercell for all calculations whenever possible.

Karsai at 14:41, 28 March 2019

2019-03-28T14:41:56Z

← Older revision		Revision as of 14:41, 28 March 2019
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	[[~~Cagtegory~~:Calculational issues]]		[[Category:Calculational issues]]

Karsai at 14:41, 28 March 2019

2019-03-28T14:41:23Z

← Older revision		Revision as of 14:41, 28 March 2019
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	[[Cagtegory:~~Technical~~ issues]]		[[Cagtegory:Calculational issues]]

Karsai: Created page with "Technical errors fall into four categories: *Errors due to k-point sampling. This will be discussed in {{TAG|k-point smearing}}. Mind that the errors due to the k-point mesh a..."

2019-03-21T14:10:24Z

Created page with "Technical errors fall into four categories: *Errors due to k-point sampling. This will be discussed in {{TAG|k-point smearing}}. Mind that the errors due to the k-point mesh a..."

New page

Technical errors fall into four categories:
*Errors due to k-point sampling. This will be discussed in {{TAG|k-point smearing}}. Mind that the errors due to the k-point mesh are not transferable i.e. a <math> 9\times 9\times 9</math> k-points grid leads to a completely different error for fcc, bcc and sc. It is therefore absolutely essential to be very careful with respect to the k-point sampling.
*Errors due to the cut-off {{TAG|ENCUT}}. This error is highly transferable, i.e. the default cutoff {{TAG|ENCUT}} (read from the {{TAG|POTCAR}} file) is in most cases safe, and one can expect that energy differences will be accurate within a few meV (see {{TAG|Energy cut off and FFT mesh}}). An exception is the stress tensor which converges notoriously slow with respect to the size of the plane wave basis set (see {{TAG|Energy vs volume Volume relaxations and Pulay stress}}).
*Wrap around errors (see {{TAG|Wrap-around errors}}): These errors are due to an insufficient FFT mesh and they are not as well behaved as the errors due to the energy cut off (see {{TAG|Energy cut off and FFT mesh}}). But once again, if one uses the default cut off (read from the {{TAG|POTCAR}} file) the wrap around errors are usually very small (a few meV per atom) even if the FFT mesh is not sufficient. The reason is that the default cut offs in VASP are rather large, and therefore the charge density and the potentials contain only small components in the region where the wrap around error occurs.
*Errors due to the real space projection: Real space projection always introduces additional (small) errors. These errors are also quite well behaved i.e. if one uses the same real space projection operators all the time, the errors are almost constants. Anyway, one should try to avoid the evaluation of energy differences between calculations with {{TAG|LREAL}}=''.FALSE.'' and {{TAG|LREAL}}=''.TRUE.'' (see {{TAG|LREAL}}). Mind that for {{ŦAG|LREAL}}=''.TRUE.'' (the recommended setting) the real space operators are optimized by VASP according to {{TAG|ENCUT}} and {{TAG|PREC}} and {{TAG|ROPT}} i.e. one gets different real space projection operators if {{TAG|ENCUT}} or {{TAG|PREC}} is changed.

In conclusion, to minimize errors one should use the same setting for {{TAG|ENCUT}}, {{TAG|ENAUG}}, {{TAG|PREC}}, {{TAG|LREAL}} and {{TAG|ROPT}} throughout all calculations, and these flags should be specified explicitly in the {{TAG|INCAR}} file. In addition it is also preferable to use the same supercell for all calculations whenever possible.

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[[Cagtegory:Technical issues]]