LTHOMAS: Difference between revisions

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{{TAGDEF|LTHOMAS|.TRUE. {{!}} .FALSE.|.FALSE.}}
{{TAGDEF|LTHOMAS|.TRUE. {{!}} .FALSE.|.FALSE.}}


Description: {{TAG|LTHOMAS}} selects a decomposition of the exchange functional based on Thomas-Fermi screening.
Description: {{TAG|LTHOMAS}} selects a decomposition of the exchange functional based on Thomas-Fermi exponential screening.
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If {{TAG|LTHOMAS}}=.TRUE. the decomposition of the exchange operator (in a range separated hybrid functional) into a short range and a long range part will be based on Thomas-Fermi screening.
If {{TAG|LTHOMAS}}=.TRUE. the decomposition of the exchange operator (in a [[Hybrid functionals: formalism|range-separated hybrid functional]]) into a short range and a long range part will be based on Thomas-Fermi exponential screening.
The Thomas-Fermi screening length ''k''<sub>TF</sub> is specified by means of the {{TAG|HFSCREEN}} tag.
The Thomas-Fermi screening length ''k''<sub>TF</sub> is specified by means of the {{TAG|HFSCREEN}} tag.


For typical semiconductors, a Thomas-Fermi screening length of about 1.8 &Aring;<sup>-1</sup> yields reasonable band gaps. In principle, however, the Thomas-Fermi screening length depends on the valence electron density; VASP determines this parameter from the number of valence electrons (read from the {{FILE|POTCAR}} file) and the volume and writes the corresponding value to the {{FILE|OUTCAR}} file:
For typical semiconductors, a Thomas-Fermi screening length of about 1.8 &Aring;<sup>-1</sup> yields reasonable band gaps. In principle, however, the Thomas-Fermi screening length depends on the valence electron density; VASP determines this parameter from the number of valence electrons (read from the {{FILE|POTCAR}} file) and the volume and writes the corresponding value to the {{FILE|OUTCAR}} file:
   Thomas-Fermi vector in A            =  2.00000
   Thomas-Fermi vector in A            =  2.00000
{{NB|mind|If {{TAG|LTHOMAS}}{{=}}.TRUE., then {{TAG|LHFCALC}}{{=}}.TRUE. is automatically set.}}
Since, VASP counts the semi-core states and ''d''-states as valence electrons, although these states do not contribute to the screening, the values reported by VASP are often incorrect.
Since, VASP counts the semi-core states and ''d''-states as valence electrons, although these states do not contribute to the screening, the values reported by VASP are often incorrect.


== Related Tags and Sections ==
== Related tags and articles ==
{{TAG|LHFCALC}},
{{TAG|LHFCALC}},
{{TAG|HFSCREEN}},
{{TAG|HFSCREEN}},
[[Hartree-Fock_and_HF/DFT_hybrid_functionals|hybrid functionals]],
{{TAG|LRHFCALC}},
[[Hartree-Fock_and_HF/DFT_hybrid_functionals#Thomas_Fermi|Thomas-Fermi screening]],
[[Hybrid functionals: formalism#Thomas-Fermi exponential screening with short-range Hartree-Fock exchange|Thomas-Fermi screening]],
[[specific_hybrid_functionals|settings for specific hybrid functionals]]
[[list_of_hybrid_functionals|List of hybrid functionals]],
[[Hybrid_functionals:_formalism|Hybrid functionals: formalism]]


{{sc|LTHOMAS|Examples|Examples that use this tag}}
{{sc|LTHOMAS|Examples|Examples that use this tag}}
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[[The_VASP_Manual|Contents]]


[[Category:INCAR]][[Category:Hybrids]]
[[Category:INCAR tag]][[Category:Exchange-correlation functionals]][[Category:Hybrid_functionals]]

Latest revision as of 11:55, 19 October 2023

LTHOMAS = .TRUE. | .FALSE.
Default: LTHOMAS = .FALSE. 

Description: LTHOMAS selects a decomposition of the exchange functional based on Thomas-Fermi exponential screening.


If LTHOMAS=.TRUE. the decomposition of the exchange operator (in a range-separated hybrid functional) into a short range and a long range part will be based on Thomas-Fermi exponential screening. The Thomas-Fermi screening length kTF is specified by means of the HFSCREEN tag.

For typical semiconductors, a Thomas-Fermi screening length of about 1.8 Å-1 yields reasonable band gaps. In principle, however, the Thomas-Fermi screening length depends on the valence electron density; VASP determines this parameter from the number of valence electrons (read from the POTCAR file) and the volume and writes the corresponding value to the OUTCAR file:

 Thomas-Fermi vector in A             =   2.00000
Mind: If LTHOMAS=.TRUE., then LHFCALC=.TRUE. is automatically set.

Since, VASP counts the semi-core states and d-states as valence electrons, although these states do not contribute to the screening, the values reported by VASP are often incorrect.

Related tags and articles

LHFCALC, HFSCREEN, LRHFCALC, Thomas-Fermi screening, List of hybrid functionals, Hybrid functionals: formalism

Examples that use this tag