EFERMI - Revision history

Csheldon: /* Related tags and articles */

2025-10-21T10:38:38Z

Csheldon: /* Related tags and articles */

2025-10-20T09:33:14Z

Huebsch at 09:31, 17 October 2024

2024-10-17T09:31:40Z

← Older revision		Revision as of 09:31, 17 October 2024
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	{{TAG\|NEDOS}}		{{TAG\|NEDOS}}

	~~----~~		[[Category:INCAR tag]][[Category:Electronic ground-state properties]]
	[[Category:INCAR tag~~]][[Category:Electronic minimization~~]][[Category:Electronic ground-state properties]]

Schlipf at 15:26, 10 June 2024

2024-06-10T15:26:30Z

← Older revision		Revision as of 15:26, 10 June 2024
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	----		----
	[[Category:INCAR tag]][[Category:Electronic minimization]][[Category:~~Density of states~~]]		[[Category:INCAR tag]][[Category:Electronic minimization]][[Category:Electronic ground-state properties]]

Huebsch at 09:21, 5 February 2024

2024-02-05T09:21:31Z

← Older revision		Revision as of 09:21, 5 February 2024
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	{{NB\|tip\| If you are interested in the properties at the Fermi energy (e.g., for transport calculations), you should compute the Fermi energy with a very dense '''k'''-point mesh. To save computational time, you can fix the charge density ({{TAG\|ICHARG}} {{=}} 11) once the Kohn-Sham states have converged with respect to the '''k'''-point density and increase the number of '''k'''-point further to converge the value of the Fermi energy.}}		{{NB\|tip\| If you are interested in the properties at the Fermi energy (e.g., for transport calculations), you should compute the Fermi energy with a very dense '''k'''-point mesh. To save computational time, you can fix the charge density ({{TAG\|ICHARG}} {{=}} 11) once the Kohn-Sham states have converged with respect to the '''k'''-point density and increase the number of '''k'''-point further to converge the value of the Fermi energy.}}
	== Fixed Fermi energy ==		== Fixed Fermi energy ==
	Occasionally, you want to compute systems with fixed Fermi energy.		Occasionally, you want to compute systems with fixed Fermi energy for a given charge density.
	To this end, set {{TAG\|EFERMI}} to a numeric value.		To this end, set {{TAG\|EFERMI}} to a numeric value and {{TAG\|ICHARG}} = 11.
	A possible use case is to set {{TAG\|EFERMI}} to the converged Fermi energy in a band-structure calculation.		A possible use case is to set {{TAG\|EFERMI}} to the converged Fermi energy in a band-structure calculation.
	You may use this to introduce electron doping/depletion to a system.		You may use this to introduce electron doping/depletion to a system.
	{{NB\|warning\|The Fermi energy cannot be computed based on '''k''' points along a path.		{{NB\|warning\|The Fermi energy cannot be computed based on '''k''' points along a path.}}
	This is, in particular, important for band-structure calculation of metallic systems because for gaped systems the Fermi energy often still ends up at a valid value within the gap despite the inaccurate computation. Hence, to plot a band structure the band energies should be taken from the calculation with fixed charge density based on '''k'''-points along a path, but the Fermi energy should be taken from the calculation based on a '''k''' mesh (e.g., the scf calculation by which the charge density was obtained or a more precisely converged Fermi energy based on the same fixed charge density). {{TAG\|EFERMI}} can fix the Fermi energy to the proper value during the band-structure calculation.}}		This is, in particular, important for band-structure calculation of metallic systems because for gaped systems the Fermi energy often still ends up at a valid value within the gap despite the inaccurate computation. Hence, to plot a band structure the band energies should be taken from the calculation with fixed charge density based on '''k'''-points along a path, but the Fermi energy should be taken from the calculation based on a '''k''' mesh (e.g., the scf calculation by which the charge density was obtained or a more precisely converged Fermi energy based on the same fixed charge density). {{TAG\|EFERMI}} can fix the Fermi energy to the proper value during the band-structure calculation.
	== Related tags and articles ==		== Related tags and articles ==
	{{TAG\|ISMEAR}},		{{TAG\|ISMEAR}},

Huebsch at 09:17, 4 February 2024

2024-02-04T09:17:37Z

← Older revision		Revision as of 09:17, 4 February 2024
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	For semiconducting materials, the Fermi energy is not uniquely defined in the bandgap of the material.		For semiconducting materials, the Fermi energy is not uniquely defined in the bandgap of the material.
	Any value that produces the correct number of electrons is allowed.		Any value that produces the correct number of electrons ({{TAG\|NELECT}}) is allowed.
	By default, VASP places the Fermi energy at a somewhat arbitrary value within the bandgap.		By default, VASP places the Fermi energy at a somewhat arbitrary value within the bandgap.
	The precise value depends on values chosen for the smearing ({{TAG\|ISMEAR}} and {{TAG\|SIGMA}}) and the density of states ({{TAG\|EMIN}}, {{TAG\|EMAX}}, and {{TAG\|NEDOS}}).		The precise value depends on values chosen for the smearing ({{TAG\|ISMEAR}} and {{TAG\|SIGMA}}) and the density of states ({{TAG\|EMIN}}, {{TAG\|EMAX}}, and {{TAG\|NEDOS}}).
	Typically this places the Fermi energy towards the bottom of the bandgap.		Typically, this places the Fermi energy towards the bottom of the bandgap.

	You can change this behavior by setting {{TAG\|EFERMI}} = MIDGAP.		You can change this behavior by setting {{TAG\|EFERMI}} = MIDGAP (recommended).
	VASP will then put the Fermi energy in the middle of the gap because this is the most consistent with increasing the smearing {{TAG\|SIGMA}}.		VASP will then put the Fermi energy in the middle of the gap because this is the most consistent with increasing the smearing {{TAG\|SIGMA}}.
	This algorithm to determine the Fermi energy was introduced in VASP.6.4.		This algorithm to determine the Fermi energy was introduced in VASP.6.4.
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	== Fermi energy in metals ==		== Fermi energy in metals ==

	~~When~~ your system does not have a gap~~, the algorithm to determine the Fermi energy is not very important~~.		MIDGAP and LEGACY should yield the same value when your system does not have a gap.
	~~Since the~~ Fermi energy is placed ~~exactly~~ at the value so that underneath are enough states to accommodate ~~all~~ electrons~~, this~~ energy ~~is well defined and both MIDGAP and LEGACY should yield~~ the ~~same value~~.		The Fermi energy is placed precisely at the value so that underneath are enough states to accommodate {{TAG\|NELECT}} electrons. The evaluation of the Fermi energy involves an integral over the 1. BZ.
	~~However~~, ~~this also means that~~ the Fermi energy ~~is now a quantity that~~ needs to be converged.		Therefore, the Fermi energy in metals needs to be converged with respect to the {{FILE\|KPOINTS}} mesh and smearing ({{TAG\|ISMEAR}}, {{TAG\|SIGMA}}).
	~~Here, you need~~ to ~~consider~~ the smearing ({{TAG\|ISMEAR}}, {{TAG\|SIGMA}}) ~~and the density of the~~ {{~~FILE~~\|~~KPOINTS}} mesh.~~		{{NB\|tip\| If you are interested in the properties at the Fermi energy (e.g., for transport calculations), you should compute the Fermi energy with a very dense '''k'''-point mesh. To save computational time, you can fix the charge density ({{TAG\|ICHARG}} {{=}} 11) once the Kohn-Sham states have converged with respect to the '''k'''-point density and increase the number of '''k'''-point further to converge the value of the Fermi energy.}}
	~~This is in particular important for band structure calculations.~~
	~~Typically, the Fermi energy of a band structure calculation will not be the same because the '''k''' points are not a well distributed mesh.~~
	If you are interested in the properties at the Fermi energy (e.g. for transport calculations), you should compute the Fermi energy with a very dense '''k'''-point mesh.
	~~Then~~, ~~correct~~ the ~~band structure calculation so that~~ the Fermi energy ~~aligns with this converged value~~.

	== Fixed Fermi energy ==		== Fixed Fermi energy ==
	Occasionally, you want to compute systems with fixed Fermi energy.		Occasionally, you want to compute systems with fixed Fermi energy.
	To this end, set {{TAG\|EFERMI}} to a numeric value.		To this end, set {{TAG\|EFERMI}} to a numeric value.
	A possible use case is to set ~~this~~ to the converged Fermi energy in a band structure calculation.		A possible use case is to set {{TAG\|EFERMI}} to the converged Fermi energy in a band-structure calculation.
	~~Keep in mind to set {{TAG\|ICHARG}} = 11 to avoid changing the number of electrons.~~		You may use this to introduce electron doping/depletion to a system.
	~~Sometimes you~~ may use this to introduce electron doping/depletion to a system.		{{NB\|warning\|The Fermi energy cannot be computed based on '''k''' points along a path.
			This is, in particular, important for band-structure calculation of metallic systems because for gaped systems the Fermi energy often still ends up at a valid value within the gap despite the inaccurate computation. Hence, to plot a band structure the band energies should be taken from the calculation with fixed charge density based on '''k'''-points along a path, but the Fermi energy should be taken from the calculation based on a '''k''' mesh (e.g., the scf calculation by which the charge density was obtained or a more precisely converged Fermi energy based on the same fixed charge density). {{TAG\|EFERMI}} can fix the Fermi energy to the proper value during the band-structure calculation.}}
	== Related ~~Tags~~ and ~~Sections~~ ==		== Related tags and articles ==
	{{TAG\|ISMEAR}},		{{TAG\|ISMEAR}},
	{{TAG\|SIGMA}},		{{TAG\|SIGMA}},
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	----		----
	~~<!-- Activate this when you want to add it to the list of INCAR tags~~		[[Category:INCAR tag]][[Category:Electronic minimization]][[Category:Density of states]]
	[[Category:INCAR]][[Category:Electronic ~~Minimization~~]][[Category:Density of ~~States~~]]
	~~-->~~

Schlipf: /* Fixed Fermi energy */

2024-02-02T15:36:09Z

Fixed Fermi energy

← Older revision		Revision as of 15:36, 2 February 2024
Line 34:		Line 34:
	A possible use case is to set this to the converged Fermi energy in a band structure calculation.		A possible use case is to set this to the converged Fermi energy in a band structure calculation.
	Keep in mind to set {{TAG\|ICHARG}} = 11 to avoid changing the number of electrons.		Keep in mind to set {{TAG\|ICHARG}} = 11 to avoid changing the number of electrons.
	Sometimes you may use this to introduce doping to a system.		Sometimes you may use this to introduce electron doping/depletion to a system.

	== Related Tags and Sections ==		== Related Tags and Sections ==

Schlipf: /* Fixed Fermi energy */

2024-02-02T15:35:53Z

Fixed Fermi energy

← Older revision		Revision as of 15:35, 2 February 2024
Line 32:		Line 32:
	Occasionally, you want to compute systems with fixed Fermi energy.		Occasionally, you want to compute systems with fixed Fermi energy.
	To this end, set {{TAG\|EFERMI}} to a numeric value.		To this end, set {{TAG\|EFERMI}} to a numeric value.
	~~Note that~~ this ~~may change~~ the number of electrons.		A possible use case is to set this to the converged Fermi energy in a band structure calculation.
			Keep in mind to set {{TAG\|ICHARG}} = 11 to avoid changing the number of electrons.
			Sometimes you may use this to introduce doping to a system.

	== Related Tags and Sections ==		== Related Tags and Sections ==

Schlipf at 15:25, 2 February 2024

2024-02-02T15:25:27Z

← Older revision		Revision as of 15:25, 2 February 2024
Line 31:		Line 31:
	== Fixed Fermi energy ==		== Fixed Fermi energy ==
	Occasionally, you want to compute systems with fixed Fermi energy.		Occasionally, you want to compute systems with fixed Fermi energy.
	To this end, set {{TAG\|EFERMI} to a numeric value.		To this end, set {{TAG\|EFERMI}} to a numeric value.
	Note that this may change the number of electrons.		Note that this may change the number of electrons.

Schlipf at 15:25, 2 February 2024

2024-02-02T15:25:15Z

← Older revision		Revision as of 15:25, 2 February 2024
Line 4:		Line 4:

	----		----

			== Fermi energy in semiconductors ==

	For semiconducting materials, the Fermi energy is not uniquely defined in the bandgap of the material.		For semiconducting materials, the Fermi energy is not uniquely defined in the bandgap of the material.
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	The value of the Fermi energy should not affect the outcome of the calculation.		The value of the Fermi energy should not affect the outcome of the calculation.

	~~Enforce~~ a particular ~~value~~ for the Fermi energy ~~by setting it~~ to a numeric value.		== Fermi energy in metals ==

			When your system does not have a gap, the algorithm to determine the Fermi energy is not very important.
			Since the Fermi energy is placed exactly at the value so that underneath are enough states to accommodate all electrons, this energy is well defined and both MIDGAP and LEGACY should yield the same value.
			However, this also means that the Fermi energy is now a quantity that needs to be converged.
			Here, you need to consider the smearing ({{TAG\|ISMEAR}}, {{TAG\|SIGMA}}) and the density of the {{FILE\|KPOINTS}} mesh.
			This is in particular important for band structure calculations.
			Typically, the Fermi energy of a band structure calculation will not be the same because the '''k''' points are not a well distributed mesh.
			If you are interested in the properties at the Fermi energy (e.g. for transport calculations), you should compute the Fermi energy with a very dense '''k'''-point mesh.
			Then, correct the band structure calculation so that the Fermi energy aligns with this converged value.

			== Fixed Fermi energy ==
			Occasionally, you want to compute systems with fixed Fermi energy.
			To this end, set {{TAG\|EFERMI} to a numeric value.
	Note that this may change the number of electrons.		Note that this may change the number of electrons.



	== Related Tags and Sections ==		== Related Tags and Sections ==

← Older revision		Revision as of 10:38, 21 October 2025
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	{{TAG\|EMAX}},		{{TAG\|EMAX}},
	{{TAG\|NEDOS}},		{{TAG\|NEDOS}},
	[[Chemical potential]]		[[Chemical potential in electron-phonon interactions]]

	[[Category:INCAR tag]][[Category:Electronic ground-state properties]]		[[Category:INCAR tag]][[Category:Electronic ground-state properties]]

← Older revision		Revision as of 09:33, 20 October 2025
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	{{TAG\|EMIN}},		{{TAG\|EMIN}},
	{{TAG\|EMAX}},		{{TAG\|EMAX}},
	{{TAG\|NEDOS}}		{{TAG\|NEDOS}},
			[[Chemical potential]]

	[[Category:INCAR tag]][[Category:Electronic ground-state properties]]		[[Category:INCAR tag]][[Category:Electronic ground-state properties]]