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| {{TAGDEF|AEXX|[real]}} | | {{TAGDEF|AEXX|[real]}} |
| {{DEF|AEXX|0.25|if {{TAG|LHFCALC}}{{=}}.TRUE.|0|otherwise}} | | {{DEF|AEXX|0.25|if {{TAG|LHFCALC}}{{=}}.TRUE.|0|if {{TAG|LHFCALC}}{{=}}.FALSE.}} |
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| Description: {{TAG|AEXX}} specifies the fraction of exact exchange in a Hartree-Fock/DFT hybrid functional type calculation. | | Description: {{TAG|AEXX}} specifies the fraction of exact exchange in a Hartree-Fock-type/hybrid-functional calculation. |
| ---- | | ---- |
| The sum of the fraction of the exact exchange and LDA exchange is always 1.0, and it is not possible to set the amount of LDA exchange indepently. Examples: if {{TAG|AEXX}}=0.25, 1/4 of the exact exchange is used, and 3/4 of the LDA exchange is added. For {{TAG|AEXX}}=0.5, half of the exact exchange is used, and one half of the LDA exchange is added.
| | {{NB|mind| |
| | *For versions of VASP prior to 6.4.0, {{TAG|ALDAX}} was constrained to be equal to 1.0-{{TAG|AEXX}}. This constraint is lifted since VASP.6.4.0. |
| | *For {{TAG|AEXX}}{{=}}1.0, VASP switches off correlation by default ({{TAG|ALDAC}}{{=}}0.0, {{TAG|AGGAC}}{{=}}0.0, and {{TAG|AMGGAC}}{{=}}0.0) and thus runs a full Hartree-Fock calculation.}} |
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| The amount of LDA correlation included in the hybrid functional can be specified through the {{TAG|ALDAC}}-tag.
| | == Related tags and articles == |
| | | {{TAG|ALDAX}}, |
| The amount of gradient correction to the exchange and the correlation contributions can be set indepently, however (some [[specific_hybrid_functionals|popular hybride functionals]] for instance use only 0.8 of the gradient contribition to the exchange). The GGA flags {{TAG|AGGAX}} and {{TAG|AGGAC}} are only used if GGA is already selected (for LDA type calculations no gradient correction will be added regardless of values is used for {{TAG|AGGAX}} and {{TAG|AGGAC}}).
| | {{TAG|ALDAC}}, |
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| '''Note''': The defaults are chosen such that the hybrid PBE0 functional is selected for PBE pseudopotentials (the PBE0 functional contains 25% of the exact exchange, and 75% of the PBE exchange, and 100% of the PBE correlation energy). The resulting expression for the exchange-correlation energy then takes the following simple form:
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| <math>
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| E_{\mathrm{xc}}^{\mathrm{PBE0}}=\frac{1}{4}~E_{\mathrm{x}}~+
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| ~\frac{3}{4}~ E_{\mathrm{x}}^{\mathrm{PBE}}
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| +~E_{\mathrm{c}}^{\mathrm{PBE}}
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| </math>
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| Other sensible values are of course {{TAG|AEXX}}=1.0 (full Hartree-Fock type calculations). In this case, VASP also automatically selects {{TAG|ALDAC}}=0.0 and {{TAG|AGGAC}}=0.0, to avoid the addition of a (semi-local) correlation energy.
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| A comprehensive evaluation of the performance of the PBE0 functional, as compared to PBE, can be found in Ref. <ref name="paier:jcp:05"/>.
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| <references>
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| <ref name="paier:jcp:05">[https://aip.scitation.org/doi/10.1063/1.1926272 J. Paier, R. Hirschl, M. Marsman, and G. Kresse, J. Chem. Phys. 122, 234102 (2005).]</ref>
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| </references>
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| == Related Tags and Sections ==
| |
| {{TAG|AGGAX}}, | | {{TAG|AGGAX}}, |
| {{TAG|AGGAC}}, | | {{TAG|AGGAC}}, |
| {{TAG|ALDAC}}, | | {{TAG|AMGGAX}}, |
| | {{TAG|AMGGAC}}, |
| {{TAG|LHFCALC}}, | | {{TAG|LHFCALC}}, |
| [[Hartree-Fock_and_HF/DFT_hybrid_functionals|hybrid functionals]], | | {{TAG|HFSCREEN}}, |
| [[specific_hybrid_functionals|settings for specific hybrid functionals]] | | [[List_of_hybrid_functionals|List of hybrid functionals]], |
| | [[Hybrid_functionals:_formalism|Hybrid functionals: formalism]] |
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| {{sc|AEXX|Examples|Examples that use this tag}} | | {{sc|AEXX|Examples|Examples that use this tag}} |
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| | == References == |
| | <references/> |
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| ---- | | ---- |
| | | [[Category:INCAR tag]][[Category:Exchange-correlation functionals]][[Category:Hybrid_functionals]] |
| [[Category:INCAR]][[Category:XC Functionals]][[Category:Hybrids]] | |
AEXX = [real]
Description: AEXX specifies the fraction of exact exchange in a Hartree-Fock-type/hybrid-functional calculation.
Mind:
- For versions of VASP prior to 6.4.0, ALDAX was constrained to be equal to 1.0-AEXX. This constraint is lifted since VASP.6.4.0.
- For AEXX=1.0, VASP switches off correlation by default (ALDAC=0.0, AGGAC=0.0, and AMGGAC=0.0) and thus runs a full Hartree-Fock calculation.
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Related tags and articles
ALDAX,
ALDAC,
AGGAX,
AGGAC,
AMGGAX,
AMGGAC,
LHFCALC,
HFSCREEN,
List of hybrid functionals,
Hybrid functionals: formalism
Examples that use this tag
References
