Category:Pseudopotentials - Revision history

Huebsch at 09:17, 14 October 2024

2024-10-14T09:17:55Z

← Older revision		Revision as of 09:17, 14 October 2024
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	[[File:Sketch Pseudopotentials.png\|300px\|right\|Sketch of a pseudopotential and pseudowavefunction]]		[[File:Sketch Pseudopotentials.png\|300px\|right\|Sketch of a pseudopotential and pseudowavefunction]]
	'''Pseudopotentials''', or effective potentials, are well-behaved potentials that replace the diverging ionic potentials. As a result, the pseudopotential approach significantly speeds up [[Electronic_minimization\|electronic structure calculations]] and makes the simulation of a wider range of materials feasible.		'''Pseudopotentials''', or effective ionic potentials, are well-behaved potentials that replace the diverging ionic potentials. As a result, the pseudopotential approach significantly speeds up [[Electronic_minimization\|electronic structure calculations]] and makes the simulation of a wider range of materials feasible.

	In a nutshell:		In a nutshell:

Wolloch: /* Theory */

2024-06-13T08:53:33Z

Theory

← Older revision		Revision as of 08:53, 13 June 2024
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	An additional approximation taken alongside the pseudopotential method is the ''frozen-core approximation''. Here, the electrons associated with an ion are separated into valence electrons ({{TAG\|ZVAL}}) that are assumed to take part in the physical/chemical property of interest and core electrons that are included as screening of the ionic potential. The separation into valence and core states depends on the property of interest and chemical bonds that occur for a specific material. For a specific atom type, VASP has a range of [[available pseudopotentials\|available pseudopotentials]] that vary in terms of core radius, the number of valence electrons, their ability to describe excited states, etc.		An additional approximation taken alongside the pseudopotential method is the ''frozen-core approximation''. Here, the electrons associated with an ion are separated into valence electrons ({{TAG\|ZVAL}}) that are assumed to take part in the physical/chemical property of interest and core electrons that are included as screening of the ionic potential. The separation into valence and core states depends on the property of interest and chemical bonds that occur for a specific material. For a specific atom type, VASP has a range of [[available pseudopotentials\|available pseudopotentials]] that vary in terms of core radius, the number of valence electrons, their ability to describe excited states, etc.

	The plane-wave coefficients of the pseudo orbitals are associated with reciprocal vectors <math>\mathbf{G}</math> in Fourier space. The number of Fourier components determines the computational cost and can be controlled by the cutoff energy ({{TAG\|ENCUT}}). The appropriate value depends on the pseudopotential and other factors. A potential is considered ''soft'' when few Fourier components are sufficient for an accurate representation, and ''hard'' otherwise. It is ~~expedient~~ to perform a convergence study on {{TAG\|ENCUT}} with respect to the quantity of interest.		The plane-wave coefficients of the pseudo orbitals are associated with reciprocal vectors <math>\mathbf{G}</math> in Fourier space. The number of Fourier components determines the computational cost and can be controlled by the cutoff energy ({{TAG\|ENCUT}}). The appropriate value depends on the pseudopotential and other factors. A potential is considered [[Available_pseudopotentials#Different_variants_specified_by_the_suffix\|''soft'']] when few Fourier components are sufficient for an accurate representation, and [[Available_pseudopotentials#Different_variants_specified_by_the_suffix\|''hard'']] otherwise. It is advised to perform a convergence study on {{TAG\|ENCUT}} with respect to the quantity of interest.

	[[Category:Calculation setup]]		[[Category:Calculation setup]]

Huebsch at 08:46, 13 June 2024

2024-06-13T08:46:26Z

← Older revision		Revision as of 08:46, 13 June 2024
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	* Simple instructions to set up a {{FILE\|POTCAR}} file with the correct format: [[Preparing a POTCAR]].		* Simple instructions to set up a {{FILE\|POTCAR}} file with the correct format: [[Preparing a POTCAR]].

	* ~~Guide~~ on ~~recommendations~~: [[Choosing pseudopotentials]].		* Recommendations on selecting potentials: [[Choosing pseudopotentials]].

	* Overview of all versions and nomenclature: [[Available pseudopotentials]]		* Overview of all versions and nomenclature: [[Available pseudopotentials]]

Huebsch at 08:07, 13 June 2024

2024-06-13T08:07:58Z

← Older revision		Revision as of 08:07, 13 June 2024
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	[[File:Sketch Pseudopotentials.png\|300px\|right\|Sketch of a pseudopotential and pseudowavefunction]]		[[File:Sketch Pseudopotentials.png\|300px\|right\|Sketch of a pseudopotential and pseudowavefunction]]
	'''Pseudopotentials''', or effective potentials, are well-behaved potentials that replace the diverging ionic potentials. As a result, the ~~[[Pseudopotential_basics\|~~pseudopotential approach]] significantly speeds up [[Electronic_minimization\|electronic structure calculations]] and makes the simulation of a wider range of materials feasible.		'''Pseudopotentials''', or effective potentials, are well-behaved potentials that replace the diverging ionic potentials. As a result, the pseudopotential approach significantly speeds up [[Electronic_minimization\|electronic structure calculations]] and makes the simulation of a wider range of materials feasible.

	In a nutshell:		In a nutshell:

Huebsch at 08:07, 13 June 2024

2024-06-13T08:07:04Z

← Older revision		Revision as of 08:07, 13 June 2024
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	[[File:Sketch Pseudopotentials.png\|300px\|right\|Sketch of a pseudopotential and pseudowavefunction]]		[[File:Sketch Pseudopotentials.png\|300px\|right\|Sketch of a pseudopotential and pseudowavefunction]]
	'''Pseudopotentials''', or effective potentials, are well-behaved potentials that replace the ionic potentials ~~that are diverging near the nuclei~~. As a result, [[Pseudopotential_basics\|~~the~~ pseudopotential approach]] significantly speeds up [[Electronic_minimization\|electronic structure calculations]] and makes the simulation of ~~more~~ materials feasible.		'''Pseudopotentials''', or effective potentials, are well-behaved potentials that replace the diverging ionic potentials. As a result, the [[Pseudopotential_basics\|pseudopotential approach]] significantly speeds up [[Electronic_minimization\|electronic structure calculations]] and makes the simulation of a wider range of materials feasible.

	~~For periodic systems it is convenient to use~~ a ~~plane-wave basis, however, describing the oscillations near the nuclei (nodal features) would necessitate an excessively high number of plane waves. Instead, one introduces pseudopotentials~~ and ~~resulting pseudo orbitals. These are identical to the true ionic potentials and orbitals outside~~ a ~~specific radius, but the pseudo orbitals contain no nodal features. Thus, the cell-periodic part of the pseudo orbitals is suitable to~~ be ~~treated~~ in a ~~plane-wave basis~~.		In a nutshell:
			* The pseudopotential and associated information required for a calculation must be present in a {{FILE\|POTCAR}} file.

	~~An additional approximation taken alongside the pseudopotential method is the ''frozen-core approximation''. Here, the electrons associated with an ion are separated into valence electrons (~~{{~~TAG~~\|~~ZVAL~~}}~~) that are assumed to take part in the physical/chemical property of interest and core electrons that are included as screening of the ionic potential in~~ the ~~pseudopotential~~.		* Simple instructions to set up a {{FILE\|POTCAR}} file with the correct format: [[Preparing a POTCAR]].

	~~The cell~~-periodic ~~part~~ of the ~~pseudo orbitals is computed in terms~~ of plane-~~wave coefficients~~, ~~or Fourier components~~, ~~associated with a reciprocal vector <math>\mathbf{G}</math>~~. ~~The maximum number of Fourier components (~~and, ~~hence~~, the ~~computational cost)~~ is ~~determined by~~ the ~~cutoff radius~~ ({{TAG\|~~ENCUT~~}}). The ~~appropriate value~~ depends on the ~~system~~ and ~~the selected pseudopotential~~. For a specific atom type, ~~there are~~ [[available pseudopotentials\|~~multiple~~ pseudopotentials ~~available~~]] that vary in terms of core radius, the number of electrons, their ability to describe excited states, etc. A potential is considered ''soft'' when few Fourier components are sufficient for an accurate representation, and ''hard'' otherwise.		* Guide on recommendations: [[Choosing pseudopotentials]].

			* Overview of all versions and nomenclature: [[Available pseudopotentials]]

			==Theory==
			VASP employs the [[projector-augmented-wave formalism\|projector-augmented-wave (PAW) method]] that uses a plane-wave basis. A plane-wave basis is most convenient for periodic systems, however without the help of '''pseudopotentials''' the description of oscillations near the nuclei (nodal features) would necessitate an excessively high number of plane waves. The PAW method introduces a mixed basis where the Kohn-Sham (KS) orbitals are decomposed in three contributions: The pseudo orbitals, pseudo-onsite orbitals and all-electron onsite orbitals. The PAW potentials and resulting pseudo orbitals are identical to the true ionic potentials and KS orbitals outside a specific radius, as illustrated in the figure. These pseudo orbitals contain no nodal features and are, thus, given in a plane-wave basis. Inside the PAW spheres the nodal features are reintroduced on a radial logarithmic grid by subtracting the pseudo-onsite orbitals and adding the all-electron onsite orbitals.

			An additional approximation taken alongside the pseudopotential method is the ''frozen-core approximation''. Here, the electrons associated with an ion are separated into valence electrons ({{TAG\|ZVAL}}) that are assumed to take part in the physical/chemical property of interest and core electrons that are included as screening of the ionic potential. The separation into valence and core states depends on the property of interest and chemical bonds that occur for a specific material. For a specific atom type, VASP has a range of [[available pseudopotentials\|available pseudopotentials]] that vary in terms of core radius, the number of valence electrons, their ability to describe excited states, etc.

			The plane-wave coefficients of the pseudo orbitals are associated with reciprocal vectors <math>\mathbf{G}</math> in Fourier space. The number of Fourier components determines the computational cost and can be controlled by the cutoff energy ({{TAG\|ENCUT}}). The appropriate value depends on the pseudopotential and other factors. A potential is considered ''soft'' when few Fourier components are sufficient for an accurate representation, and ''hard'' otherwise. It is expedient to perform a convergence study on {{TAG\|ENCUT}} with respect to the quantity of interest.

			[[Category:Calculation setup]]

Wolloch at 13:12, 12 June 2024

2024-06-12T13:12:56Z

← Older revision	Revision as of 13:12, 12 June 2024
Line 1:	Line 1:
		[[File:Sketch Pseudopotentials.png\|300px\|right\|Sketch of a pseudopotential and pseudowavefunction]]
		'''Pseudopotentials''', or effective potentials, are well-behaved potentials that replace the ionic potentials that are diverging near the nuclei. As a result, [[Pseudopotential_basics\|the pseudopotential approach]] significantly speeds up [[Electronic_minimization\|electronic structure calculations]] and makes the simulation of more materials feasible.

		For periodic systems it is convenient to use a plane-wave basis, however, describing the oscillations near the nuclei (nodal features) would necessitate an excessively high number of plane waves. Instead, one introduces pseudopotentials and resulting pseudo orbitals. These are identical to the true ionic potentials and orbitals outside a specific radius, but the pseudo orbitals contain no nodal features. Thus, the cell-periodic part of the pseudo orbitals is suitable to be treated in a plane-wave basis.

		An additional approximation taken alongside the pseudopotential method is the ''frozen-core approximation''. Here, the electrons associated with an ion are separated into valence electrons ({{TAG\|ZVAL}}) that are assumed to take part in the physical/chemical property of interest and core electrons that are included as screening of the ionic potential in the pseudopotential.

		The cell-periodic part of the pseudo orbitals is computed in terms of plane-wave coefficients, or Fourier components, associated with a reciprocal vector <math>\mathbf{G}</math>. The maximum number of Fourier components (and, hence, the computational cost) is determined by the cutoff radius ({{TAG\|ENCUT}}). The appropriate value depends on the system and the selected pseudopotential. For a specific atom type, there are [[available pseudopotentials\|multiple pseudopotentials available]] that vary in terms of core radius, the number of electrons, their ability to describe excited states, etc. A potential is considered ''soft'' when few Fourier components are sufficient for an accurate representation, and ''hard'' otherwise.

Huebsch: Created blank page

2024-06-11T09:54:12Z

Created blank page

New page

← Older revision		Revision as of 08:07, 13 June 2024
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	[[File:Sketch Pseudopotentials.png\|300px\|right\|Sketch of a pseudopotential and pseudowavefunction]]		[[File:Sketch Pseudopotentials.png\|300px\|right\|Sketch of a pseudopotential and pseudowavefunction]]
	'''Pseudopotentials''', or effective potentials, are well-behaved potentials that replace the ionic potentials ~~that are diverging near the nuclei~~. As a result, [[Pseudopotential_basics\|~~the~~ pseudopotential approach]] significantly speeds up [[Electronic_minimization\|electronic structure calculations]] and makes the simulation of ~~more~~ materials feasible.		'''Pseudopotentials''', or effective potentials, are well-behaved potentials that replace the diverging ionic potentials. As a result, the [[Pseudopotential_basics\|pseudopotential approach]] significantly speeds up [[Electronic_minimization\|electronic structure calculations]] and makes the simulation of a wider range of materials feasible.

	~~For periodic systems it is convenient to use~~ a ~~plane-wave basis, however, describing the oscillations near the nuclei (nodal features) would necessitate an excessively high number of plane waves. Instead, one introduces pseudopotentials~~ and ~~resulting pseudo orbitals. These are identical to the true ionic potentials and orbitals outside~~ a ~~specific radius, but the pseudo orbitals contain no nodal features. Thus, the cell-periodic part of the pseudo orbitals is suitable to~~ be ~~treated~~ in a ~~plane-wave basis~~.		In a nutshell:
			* The pseudopotential and associated information required for a calculation must be present in a {{FILE\|POTCAR}} file.

	~~An additional approximation taken alongside the pseudopotential method is the ''frozen-core approximation''. Here, the electrons associated with an ion are separated into valence electrons (~~{{~~TAG~~\|~~ZVAL~~}}~~) that are assumed to take part in the physical/chemical property of interest and core electrons that are included as screening of the ionic potential in~~ the ~~pseudopotential~~.		* Simple instructions to set up a {{FILE\|POTCAR}} file with the correct format: [[Preparing a POTCAR]].

	~~The cell~~-periodic ~~part~~ of the ~~pseudo orbitals is computed in terms~~ of plane-~~wave coefficients~~, ~~or Fourier components~~, ~~associated with a reciprocal vector <math>\mathbf{G}</math>~~. ~~The maximum number of Fourier components (~~and, ~~hence~~, the ~~computational cost)~~ is ~~determined by~~ the ~~cutoff radius~~ ({{TAG\|~~ENCUT~~}}). The ~~appropriate value~~ depends on the ~~system~~ and ~~the selected pseudopotential~~. For a specific atom type, ~~there are~~ [[available pseudopotentials\|~~multiple~~ pseudopotentials ~~available~~]] that vary in terms of core radius, the number of electrons, their ability to describe excited states, etc. A potential is considered ''soft'' when few Fourier components are sufficient for an accurate representation, and ''hard'' otherwise.		* Guide on recommendations: [[Choosing pseudopotentials]].

			* Overview of all versions and nomenclature: [[Available pseudopotentials]]

			==Theory==
			VASP employs the [[projector-augmented-wave formalism\|projector-augmented-wave (PAW) method]] that uses a plane-wave basis. A plane-wave basis is most convenient for periodic systems, however without the help of '''pseudopotentials''' the description of oscillations near the nuclei (nodal features) would necessitate an excessively high number of plane waves. The PAW method introduces a mixed basis where the Kohn-Sham (KS) orbitals are decomposed in three contributions: The pseudo orbitals, pseudo-onsite orbitals and all-electron onsite orbitals. The PAW potentials and resulting pseudo orbitals are identical to the true ionic potentials and KS orbitals outside a specific radius, as illustrated in the figure. These pseudo orbitals contain no nodal features and are, thus, given in a plane-wave basis. Inside the PAW spheres the nodal features are reintroduced on a radial logarithmic grid by subtracting the pseudo-onsite orbitals and adding the all-electron onsite orbitals.

			An additional approximation taken alongside the pseudopotential method is the ''frozen-core approximation''. Here, the electrons associated with an ion are separated into valence electrons ({{TAG\|ZVAL}}) that are assumed to take part in the physical/chemical property of interest and core electrons that are included as screening of the ionic potential. The separation into valence and core states depends on the property of interest and chemical bonds that occur for a specific material. For a specific atom type, VASP has a range of [[available pseudopotentials\|available pseudopotentials]] that vary in terms of core radius, the number of valence electrons, their ability to describe excited states, etc.

			The plane-wave coefficients of the pseudo orbitals are associated with reciprocal vectors <math>\mathbf{G}</math> in Fourier space. The number of Fourier components determines the computational cost and can be controlled by the cutoff energy ({{TAG\|ENCUT}}). The appropriate value depends on the pseudopotential and other factors. A potential is considered ''soft'' when few Fourier components are sufficient for an accurate representation, and ''hard'' otherwise. It is expedient to perform a convergence study on {{TAG\|ENCUT}} with respect to the quantity of interest.

			[[Category:Calculation setup]]