Fermi level - Revision history

BrianMcMahon: Tidied translations and added German and Spanish (U. Mueller)

2017-11-13T13:24:16Z

Tidied translations and added German and Spanish (U. Mueller)

MassimoNespolo: Languages

2017-09-13T14:34:47Z

Languages

BrianMcMahon: Style edits to align with printed edition

2017-05-19T13:12:07Z

Style edits to align with printed edition

BrianMcMahon: moved Fermi energy to Fermi level: Synonyms

2016-04-13T11:40:38Z

moved Fermi energy to Fermi level: Synonyms

BrianMcMahon: Created page with "== Definition == The '''Fermi level''' is also known as the '''Fermi energy'''. Two definitions are proposed; the first concentrates on a general formal definition while the sec..."

2016-04-13T11:40:17Z

Created page with "== Definition == The '''Fermi level''' is also known as the '''Fermi energy'''. Two definitions are proposed; the first concentrates on a general formal definition while the sec..."

New page

== Definition ==

The '''Fermi level''' is also known as the '''Fermi energy'''. Two definitions are proposed; the first concentrates on a general formal definition while the second focusses on theoretical convergence for use by XAS users and programs.

(1) In an independent particle approach to the description of a fermion system (''i.e.'' particles obeying Pauli’s exclusion principle), the '''Fermi level''' is the energy value lying between the highest occupied level and the lowest unoccupied level, usually defined as their average. If the energy level spectrum is a continuum (or almost a continuum) the three levels coincide. In a many-body approach, the Fermi level is the energy necessary for adding or subtracting a particle from the system. This definition encompasses the non interacting case.

Like all energy states, the Fermi level is measured from the vacuum level. In XAS spectra the Fermi level is below or at the first allowed transition, depending on the system and the absorption edge.

(2) In X-ray absorption spectroscopy (XAS), the '''Fermi energy''' dictates possible pre-edge features and explains the possibility or impossibility of open scattering channels adding to the near-edge structure. When theoretical formalisms compute the reference Fermi energy, crucial for the XANES region, the convergence of the complete quantum mechanical system is an absolute requirement, whether atomic, cluster, or periodic boundary conditions are used. The lack of convergence for theoretical formalisms can at this time lead to systematic errors in the determination of the Fermi energy and corresponding pre-edge structure of order 1-10 eV in the X-ray regime
and should be considered carefully as this affects the interpretation of XAFS and XANES.

[[Category:X-ray absorption spectroscopy]]

← Older revision		Revision as of 13:24, 13 November 2017
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−	<font color="blue">Niveau de Fermi</font> (''Fr''); <font color="~~green~~">~~Energía de~~ Fermi</font> (''Sp''); <font color="~~red~~">Fermi~~-Niveau~~</font> (''Ge''); <font color="~~black~~">~~Livello di Fermi~~</font> (''It''); <font color="~~brown~~">~~Энергия Ферми~~</font> (''Ru''); <font color="~~purple~~">~~フェルミ準位~~</font> (''Ja'').	+	<font color="blue">Niveau de Fermi</font> (''Fr''). <font color="red">Fermi-Energie, Fermi-Niveau</font> (''Ge''). <font color="black">Livello di Fermi</font> (''It''). <font color="brown">Энергия Ферми</font> (''Ru''). <font color="purple">フェルミ準位</font> (''Ja''). <font color="green">Nivel de Fermi, Energía de Fermi</font> (''Sp'').

	== Definition ==		== Definition ==

← Older revision		Revision as of 14:34, 13 September 2017
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		+	<font color="blue">Niveau de Fermi</font> (''Fr''); <font color="green">Energía de Fermi</font> (''Sp''); <font color="red">Fermi-Niveau</font> (''Ge''); <font color="black">Livello di Fermi</font> (''It''); <font color="brown">Энергия Ферми</font> (''Ru''); <font color="purple">フェルミ準位</font> (''Ja'').
		+
	== Definition ==		== Definition ==

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 The '''Fermi level''' is also known as the '''Fermi energy'''. Two definitions are proposed; the first concentrates on a general formal definition while the second focusses on theoretical convergence for use by XAS users and programs.
-(1) In an independent particle approach to the description of a fermion system (''i.e.'' particles obeying Pauli’s exclusion principle), the '''Fermi level''' is the energy value lying between the highest occupied level and the lowest unoccupied level, usually defined as their average. If the energy level spectrum is a continuum (or almost a continuum) the three levels coincide. In a many-body approach, the Fermi level is the energy necessary for adding or subtracting a particle from the system. This definition encompasses the non interacting case.
+(1) In an independent particle approach to the description of a fermion system (''i.e.'' particles obeying Pauli’s exclusion principle), the '''Fermi level''' is the energy value lying between the highest occupied level and the lowest unoccupied level, usually defined as their average. If the energy level spectrum is a continuum (or almost a continuum) the three levels coincide. In a many-body approach, the Fermi level is the energy necessary for adding or subtracting a particle from the system. This definition encompasses the non-interacting case.
 Like all energy states, the Fermi level is measured from the vacuum level. In XAS spectra the Fermi level is below or at the first allowed transition, depending on the system and the absorption edge.

← Older revision	Revision as of 11:40, 13 April 2016
(No difference)