LTHOMAS: Difference between revisions
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Description: {{TAG|LTHOMAS}} selects a decomposition of the exchange functional based on Thomas-Fermi exponential 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 Å<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 Å<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. | ||
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{{TAG|HFSCREEN}}, | {{TAG|HFSCREEN}}, | ||
{{TAG|LRHFCALC}}, | {{TAG|LRHFCALC}}, | ||
[[Hybrid functionals: formalism# | [[Hybrid functionals: formalism#Thomas-Fermi exponential screening with short-range Hartree-Fock exchange|Thomas-Fermi screening]], | ||
[[list_of_hybrid_functionals|List of hybrid functionals]], | [[list_of_hybrid_functionals|List of hybrid functionals]], | ||
[[Hybrid_functionals:_formalism|Hybrid functionals: formalism]] | [[Hybrid_functionals:_formalism|Hybrid functionals: formalism]] | ||
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