Choosing pseudopotentials - Revision history

Huebsch: /* Aspects to refine the choice of pseudopotentials */

2024-06-26T11:57:01Z

Aspects to refine the choice of pseudopotentials

← Older revision		Revision as of 11:57, 26 June 2024
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	==Aspects to refine the choice of pseudopotentials==		==Aspects to refine the choice of pseudopotentials==

	'''Aspect 1:''' ~~Analyze the geometry of your structure for short bonds~~ and the valency of the ions.		'''Aspect 1:''' The bond lengths and the valency of the ions.

	:Short bonds will require harder potentials, and semicore states might have to be treated as valence for certain chemical bonding. For some elements, variants for specific valency exist; for example, the suffix [[Available_pseudopotentials#Different_variants_specified_by_the_suffix\|_2 or _3]] can be used to describe [[#Lanthanides with fixed valence\| fixed divalent or trivalent Lanthanides]].		:Short bonds will require harder potentials, and semicore states might have to be treated as valence for certain chemical bonding. For some elements, variants for specific valency exist; for example, the suffix [[Available_pseudopotentials#Different_variants_specified_by_the_suffix\|_2 or _3]] can be used to describe [[#Lanthanides with fixed valence\| fixed divalent or trivalent Lanthanides]].

	'''Aspect 2:''' ~~Consider the~~ physical or chemical property ~~that is the objective~~ of ~~your calculation~~.		'''Aspect 2:''' The physical or chemical property of interest.

	:If you are only interested in a rough [[Ionic minimization\|structure optimization]], soft potentials ([[Available_pseudopotentials#Different_variants_specified_by_the_suffix\|_s]]) with minimal valency may suffice. This approach might also work for [[Phonons\|phonon calculations]] that rely on large supercells.		:If you are only interested in a rough [[Ionic minimization\|structure optimization]], soft potentials ([[Available_pseudopotentials#Different_variants_specified_by_the_suffix\|_s]]) with minimal valency may suffice. This approach might also work for [[Phonons\|phonon calculations]] that rely on large supercells.
	:On the other hand, when optimizing a magnetic structure, it may be necessary to include semicore states in the valence ([[Available_pseudopotentials#Different_variants_specified_by_the_suffix\|_pv and _sv]]).		:On the other hand, when optimizing a magnetic structure, it may be necessary to include semicore states in the valence ([[Available_pseudopotentials#Different_variants_specified_by_the_suffix\|_pv and _sv]]).
	:For the computation of [[optical properties]], it is crucial to use [[Available pseudopotentials#GW potentials\|GW potentials]].		:For the computation of [[optical properties]], it is crucial to use [[Available pseudopotentials#GW potentials\|GW potentials]].

	'''Aspect 3:''' ~~Scrutinize the requirements of the~~ method or algorithm used in your calculation.		'''Aspect 3:''' The method or algorithm used in your calculation.

	:For any calculation involving unoccupied states significantly above the Fermi energy, the [[Available_pseudopotentials#Different_variants_specified_by_the_suffix\|_GW variants]] of potentials are superior and should be used. Particularly, all kinds of [[Many-body perturbation theory\|calculations within many-body perturbation theory]] need a high number of [[NBANDS#Many-body_perturbation_theory_calculations\|empty bands]]. Therefore, when GW, BSE, etc. is performed, the [[Available pseudopotentials#GW potentials\|GW potentials]] should be used throughout the workflow.		:For any calculation involving unoccupied states significantly above the Fermi energy, the [[Available_pseudopotentials#Different_variants_specified_by_the_suffix\|_GW variants]] of potentials are superior and should be used. Particularly, all kinds of [[Many-body perturbation theory\|calculations within many-body perturbation theory]] need a high number of [[NBANDS#Many-body_perturbation_theory_calculations\|empty bands]]. Therefore, when GW, BSE, etc. is performed, the [[Available pseudopotentials#GW potentials\|GW potentials]] should be used throughout the workflow.

Huebsch: /* Related tags and sections */

2024-06-20T06:15:39Z

Related tags and sections

← Older revision		Revision as of 06:15, 20 June 2024
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	{{FILE\|POTCAR}}, [[Prepare a POTCAR]], [[Available pseudopotentials]]		{{FILE\|POTCAR}}, [[Prepare a POTCAR]], [[Available pseudopotentials]]

	Theoretical background: [[Pseudopotentials~~]], [[Pseudopotential basics~~]], [[Projector-augmented-wave formalism]]		Theoretical background: [[Pseudopotentials]], [[Projector-augmented-wave formalism]]

			==References==

	[[Category:Pseudopotentials]][[Category:Howto]]		[[Category:Pseudopotentials]][[Category:Howto]]

Wolloch: /* Recommendations and advice */

2024-06-13T09:41:08Z

Recommendations and advice

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	:The following table highlights recommended PAW potentials for calculations involving many states above the Fermi energy in '''bold'''.		:The following table highlights recommended PAW potentials for calculations involving many states above the Fermi energy in '''bold'''.
	:They are optimized for scattering properties high above the Fermi level and thus have advantages if many unoccupied states are involved, as for [[optical properties]] or [[many-body perturbation theory]]. Some results indicate that these GW potentials are also more accurate for ground-state-DFT calculations{{cite\|bosoni:natphysrev:2023}}, but the results should be very comparable with the standard potentials in most cases. Unless the uttermost accuracy is required, it is usually not worth paying the extra computational cost required<ref>For the potpaw_PBE.64 potential set, {{TAG\|ENMAX}} is on average ~26 eV (~11%) and {{TAG\|EAUG}} ~210 eV (42%) larger for the GW potentials compared to their standard counterparts with the same valency.</ref> for the GW potentials compared to their standard counterparts.		:They are optimized for scattering properties high above the Fermi level and thus have advantages if many unoccupied states are involved, as for [[optical properties]] or [[many-body perturbation theory]]. Some results indicate that these GW potentials are also more accurate for ground-state-DFT calculations{{cite\|bosoni:natphysrev:2023}}, but the results should be very comparable with the standard potentials in most cases. Unless the uttermost accuracy is required, it is usually not worth paying the extra computational cost required<ref>For the potpaw_PBE.64 potential set, {{TAG\|ENMAX}} is on average ~26 eV (~11%) and {{TAG\|EAUG}} ~210 eV (~42%) larger for the GW potentials compared to their standard counterparts with the same valency.</ref> for the GW potentials compared to their standard counterparts.

	:{\| class="wikitable sortable mw-collapsible mw-collapsed"		:{\| class="wikitable sortable mw-collapsible mw-collapsed"

Wolloch: /* Recommendations and advice */

2024-06-13T09:19:48Z

Recommendations and advice

← Older revision		Revision as of 09:19, 13 June 2024
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	:The following table highlights recommended PAW potentials for calculations involving many states above the Fermi energy in '''bold'''.		:The following table highlights recommended PAW potentials for calculations involving many states above the Fermi energy in '''bold'''.
	:~~These potentials are not necessarily superior (and even might be inferior) for calculations involving mostly occupied states, e.g., for [[Ionic_minimization\|structural relaxations]] or [[phonons]].~~ They are optimized for scattering properties high above the Fermi level and thus have advantages if many unoccupied states are involved, as for [[optical properties]] or [[many-body perturbation theory]].		:They are optimized for scattering properties high above the Fermi level and thus have advantages if many unoccupied states are involved, as for [[optical properties]] or [[many-body perturbation theory]]. Some results indicate that these GW potentials are also more accurate for ground-state-DFT calculations{{cite\|bosoni:natphysrev:2023}}, but the results should be very comparable with the standard potentials in most cases. Unless the uttermost accuracy is required, it is usually not worth paying the extra computational cost required<ref>For the potpaw_PBE.64 potential set, {{TAG\|ENMAX}} is on average ~26 eV (~11%) and {{TAG\|EAUG}} ~210 eV (42%) larger for the GW potentials compared to their standard counterparts with the same valency.</ref> for the GW potentials compared to their standard counterparts.

	:{\| class="wikitable sortable mw-collapsible mw-collapsed"		:{\| class="wikitable sortable mw-collapsible mw-collapsed"

Wolloch: /* Related tags and sections */

2024-06-12T14:09:39Z

Related tags and sections

← Older revision		Revision as of 14:09, 12 June 2024
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	{{FILE\|POTCAR}}, [[Prepare a POTCAR]], [[Available pseudopotentials]]		{{FILE\|POTCAR}}, [[Prepare a POTCAR]], [[Available pseudopotentials]]

	Theoretical background: [[Pseudopotentials]], [[~~Theory:~~ Pseudopotential basics]], [[Projector-augmented-wave formalism]]		Theoretical background: [[Pseudopotentials]], [[Pseudopotential basics]], [[Projector-augmented-wave formalism]]

	[[Category:Pseudopotentials]][[Category:Howto]]		[[Category:Pseudopotentials]][[Category:Howto]]

Wolloch: /* f-elements */

2024-06-12T14:02:15Z

f-elements

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	:Particularly problematic is the description of the transition from an itinerant (band-like) behavior observed at the beginning of each period to localized states towards the end of the period. For the 4<i>f</i> elements, this transition occurs already in La and Ce, whereas the transition sets in for Pu and Am for the 5<i>f</i> elements. A routine way to cope with the inabilities of present DFT functionals to describe the localized 4<i>f</i> electrons is to place the 4<i>f</i> electrons in the core. Such potentials are available and described below; however, they are expected to fail to describe magnetic properties arising <i>f</i> orbitals. Furthermore, PAW potentials in which the <i>f</i> states are treated as valence states are available, but these potentials are expected to fail to describe electronic properties when <i>f</i> electrons are localized. In this case, one might treat electronic correlation effects more carefully, e.g., by employing hybrid functionals or introducing on-site Coulomb interaction.		:Particularly problematic is the description of the transition from an itinerant (band-like) behavior observed at the beginning of each period to localized states towards the end of the period. For the 4<i>f</i> elements, this transition occurs already in La and Ce, whereas the transition sets in for Pu and Am for the 5<i>f</i> elements. A routine way to cope with the inabilities of present DFT functionals to describe the localized 4<i>f</i> electrons is to place the 4<i>f</i> electrons in the core. Such potentials are available and described below; however, they are expected to fail to describe magnetic properties arising <i>f</i> orbitals. Furthermore, PAW potentials in which the <i>f</i> states are treated as valence states are available, but these potentials are expected to fail to describe electronic properties when <i>f</i> electrons are localized. In this case, one might treat electronic correlation effects more carefully, e.g., by employing hybrid functionals or introducing on-site Coulomb interaction.

	:For some elements, soft versions (_s) are available as well. The semi-core <i>p</i> states are always treated as valence states, whereas the semi-core <i>s</i> states are treated as valence states only in the standard potentials. For most applications (oxides, sulfides), the standard version should be used since the soft versions might result in <i>s</i> ghost-states close to the Fermi-level (,e.g., Ce_s in ceria). The soft versions are, however, expected to be sufficiently accurate for calculations on intermetallic compounds.		:For some elements, [[Available_pseudopotentials#Different_variants_specified_by_the_suffix\|soft versions (_s)]] are available as well. The semi-core <i>p</i> states are always treated as valence states, whereas the semi-core <i>s</i> states are treated as valence states only in the standard potentials. For most applications (oxides, sulfides), the standard version should be used since the soft versions might result in <i>s</i> ghost-states close to the Fermi-level (,e.g., Ce_s in ceria). The soft versions are, however, expected to be sufficiently accurate for calculations on intermetallic compounds.

	====Lanthanides with fixed valence====		====Lanthanides with fixed valence====

Wolloch: /* d-elements */

2024-06-12T14:01:23Z

d-elements

← Older revision		Revision as of 14:01, 12 June 2024
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	:For the <i>d</i> elements, applies the same as for the alkali and earth-alkali metals: the semi-core <i>p</i> states and possibly the semi-core <i>s</i> states should be treated as valence states. In most cases, however, reliable results can be obtained even if the semi-core states are kept frozen.		:For the <i>d</i> elements, applies the same as for the alkali and earth-alkali metals: the semi-core <i>p</i> states and possibly the semi-core <i>s</i> states should be treated as valence states. In most cases, however, reliable results can be obtained even if the semi-core states are kept frozen.

	:When to switch from X_pv potentials to the X potentials depends on the required accuracy and the row for the 3<i>d</i> elements, even the Ti, V, and Cr potentials give reasonable results but should be used with uttermost care. 4<i>d</i> elements are the most problematic, and we advise using the X_pv potentials up to Tc_pv. For 5<i>d</i> elements the 5<i>p</i> states are rather strongly localized (below 3 Ry), since the 4<i>f</i> shell becomes filled. One can use the standard potentials starting from Hf, but we recommend performing test calculations. For some elements, X_sv potentials are available (,e.g., Nb_sv, Mo_sv, Hf_sv). These potentials usually have very similar energy cutoffs as the _pv potentials and can also be used. For HF-type and hybrid-functional calculations, we strongly recommend using the _sv and _pv potentials whenever possible.		:When to switch from X_pv potentials to the X potentials depends on the required accuracy and the row for the 3<i>d</i> elements, even the Ti, V, and Cr potentials give reasonable results but should be used with uttermost care. 4<i>d</i> elements are the most problematic, and we advise using the X_pv potentials up to Tc_pv. For 5<i>d</i> elements the 5<i>p</i> states are rather strongly localized (below 3 Ry), since the 4<i>f</i> shell becomes filled. One can use the standard potentials starting from Hf, but we recommend performing test calculations. For some elements, X_sv potentials are available (,e.g., Nb_sv, Mo_sv, Hf_sv). These potentials usually have very similar energy cutoffs as the _pv potentials and can also be used. For HF-type and hybrid-functional calculations, we strongly recommend using the [[Available_pseudopotentials#Different_variants_specified_by_the_suffix\|_sv and _pv]] potentials whenever possible.
	{{NB\|tip\|As a rule of thumb the <i>p</i> states should be treated as valence states for d-elements, if their eigenenergy <math>\epsilon</math> lies above 3 Ry.\|:}}		{{NB\|tip\|As a rule of thumb the <i>p</i> states should be treated as valence states for d-elements, if their eigenenergy <math>\epsilon</math> lies above 3 Ry.\|:}}

Wolloch: /* First-row elements */

2024-06-12T13:58:15Z

First-row elements

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	===First-row elements===		===First-row elements===

	:For the 1st row elements B, C, N, O, and F, three potential versions exist, the plain one, a hard version, and a soft version. For most purposes, the standard version of PAW potentials is most appropriate. They yield reliable results for energy cutoffs between 325 and 400 eV, where 370-400 eV are required to predict vibrational properties accurately. Binding geometries and energy differences are already well reproduced at 325 eV. The typical bond-length errors for first row dimers (N<sub>2</sub>, CO, O<sub>2</sub>) are about 1% compared to more accurate DFT calculations. The hard pseudopotentials _h give results that are essentially identical to the best DFT calculations presently available (FLAPW, or Gaussian with very large basis sets). The soft potentials are optimized to work around 250-280 eV. They yield reliable description for most oxides, such as V<sub>x</sub>O<sub>y</sub>, TiO<sub>2</sub>, CeO<sub>2</sub>, but fail to describe some structural details in zeolites, i.e., cell parameters, and volume.		:For the 1st row elements B, C, N, O, and F, three potential versions exist, the plain one, a hard version, and a soft version. For most purposes, the standard version of PAW potentials is most appropriate. They yield reliable results for energy cutoffs between 325 and 400 eV, where 370-400 eV are required to predict vibrational properties accurately. Binding geometries and energy differences are already well reproduced at 325 eV. The typical bond-length errors for first row dimers (N<sub>2</sub>, CO, O<sub>2</sub>) are about 1% compared to more accurate DFT calculations. The [[Available_pseudopotentials#Different_variants_specified_by_the_suffix\|hard pseudopotentials (_h)]] give results that are essentially identical to the best DFT calculations presently available (FLAPW, or Gaussian with very large basis sets). The [[Available_pseudopotentials#Different_variants_specified_by_the_suffix\|soft potentials (_s)]] are optimized to work around 250-280 eV. They yield reliable description for most oxides, such as V<sub>x</sub>O<sub>y</sub>, TiO<sub>2</sub>, CeO<sub>2</sub>, but fail to describe some structural details in zeolites, i.e., cell parameters, and volume.

	:For Hartree-Fock (HF) and hybrid-functional calculations, we strictly recommend using the standard, standard GW, or hard potentials. For instance, the O_s potential can cause unacceptably large errors even in transition metal oxides. Generally, the soft potentials are less transferable from one exchange-correlation functional to another and often fail when the exact exchange needs to be calculated.		:For Hartree-Fock (HF) and hybrid-functional calculations, we strictly recommend using the standard, standard GW, or hard potentials. For instance, the O_s potential can cause unacceptably large errors even in transition metal oxides. Generally, the soft potentials are less transferable from one exchange-correlation functional to another and often fail when the exact exchange needs to be calculated.

Wolloch at 13:54, 12 June 2024

2024-06-12T13:54:29Z

← Older revision		Revision as of 13:54, 12 June 2024
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	'''Aspect 1:''' Analyze the geometry of your structure for short bonds and the valency of the ions.		'''Aspect 1:''' Analyze the geometry of your structure for short bonds and the valency of the ions.
	:Short bonds will require harder potentials, and semicore states might have to be treated as valence for certain chemical bonding. For some elements, variants for specific valency exist; for example, the suffix _2 or _3 can be used to describe [[#Lanthanides with fixed valence\| fixed divalent or trivalent Lanthanides]].		:Short bonds will require harder potentials, and semicore states might have to be treated as valence for certain chemical bonding. For some elements, variants for specific valency exist; for example, the suffix [[Available_pseudopotentials#Different_variants_specified_by_the_suffix\|_2 or _3]] can be used to describe [[#Lanthanides with fixed valence\| fixed divalent or trivalent Lanthanides]].

	'''Aspect 2:''' Consider the physical or chemical property that is the objective of your calculation.		'''Aspect 2:''' Consider the physical or chemical property that is the objective of your calculation.
	:If you are only interested in a rough [[Ionic minimization\|structure optimization]], soft potentials (_s) with minimal valency may suffice. This approach might also work for [[Phonons\|phonon calculations]] that rely on large supercells.		:If you are only interested in a rough [[Ionic minimization\|structure optimization]], soft potentials ([[Available_pseudopotentials#Different_variants_specified_by_the_suffix\|_s]]) with minimal valency may suffice. This approach might also work for [[Phonons\|phonon calculations]] that rely on large supercells.
	:On the other hand, when optimizing a magnetic structure, it may be necessary to include semicore states in the valence (_pv and _sv).		:On the other hand, when optimizing a magnetic structure, it may be necessary to include semicore states in the valence ([[Available_pseudopotentials#Different_variants_specified_by_the_suffix\|_pv and _sv]]).
	:For the computation of [[optical properties]], it is crucial to use [[Available pseudopotentials#GW potentials\|GW potentials]].		:For the computation of [[optical properties]], it is crucial to use [[Available pseudopotentials#GW potentials\|GW potentials]].

	'''Aspect 3:''' Scrutinize the requirements of the method or algorithm used in your calculation.		'''Aspect 3:''' Scrutinize the requirements of the method or algorithm used in your calculation.
	:For any calculation involving unoccupied states significantly above the Fermi energy, the _GW variants of potentials are superior and should be used. Particularly, all kinds of [[Many-body perturbation theory\|calculations within many-body perturbation theory]] need a high number of [[NBANDS#Many-body_perturbation_theory_calculations\|empty bands]]. Therefore, when GW, BSE, etc. is performed, the [[Available pseudopotentials#GW potentials\|GW potentials]] should be used throughout the workflow.		:For any calculation involving unoccupied states significantly above the Fermi energy, the [[Available_pseudopotentials#Different_variants_specified_by_the_suffix\|_GW variants]] of potentials are superior and should be used. Particularly, all kinds of [[Many-body perturbation theory\|calculations within many-body perturbation theory]] need a high number of [[NBANDS#Many-body_perturbation_theory_calculations\|empty bands]]. Therefore, when GW, BSE, etc. is performed, the [[Available pseudopotentials#GW potentials\|GW potentials]] should be used throughout the workflow.

	:[[Hybrid_functionals\|Hartree-Fock and hybrid caluclations]] should ''not'' be performed with soft potentials (_s). Moreover, any calculations where you switch the [[exchange-correlation functional]] should ''not'' be performed with soft potentials (_s).		:[[Hybrid_functionals\|Hartree-Fock and hybrid caluclations]] should ''not'' be performed with soft potentials ([[Available_pseudopotentials#Different_variants_specified_by_the_suffix\|_s]]). Moreover, any calculations where you switch the [[exchange-correlation functional]] should ''not'' be performed with soft potentials ([[Available_pseudopotentials#Different_variants_specified_by_the_suffix\|_s]]).

	:For standard DFT-ground-state calculations, using _GW or _h potentials is usually unnecessary unless, e.g., the property of interest or geometry of the structure demands it.		:For standard DFT-ground-state calculations, using [[Available_pseudopotentials#Different_variants_specified_by_the_suffix\|_GW or _h]] potentials is usually unnecessary unless, e.g., the property of interest or geometry of the structure demands it.

	==Recommendations and advice==		==Recommendations and advice==

Huebsch: /* Recommended PAW potentials */

2024-06-12T09:54:15Z

Recommended PAW potentials

← Older revision		Revision as of 09:54, 12 June 2024
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	:{\| class="wikitable sortable mw-collapsible mw-collapsed"		:{\| class="wikitable sortable mw-collapsible mw-collapsed"
	\| colspan="4" style="text-align:center"\| GW potentials		\| colspan="4" style="text-align:center"\| GW potentials (potpaw.64)
	\|-		\|-
	! Potential name !! Number of valence electrons !! Valence electron configuration !! ENAMX [eV]		! Potential name !! Number of valence electrons !! Valence electron configuration !! ENAMX [eV]