LTHOMAS: Difference between revisions

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{{TAG|LHFCALC}},
{{TAG|LHFCALC}},
{{TAG|HFSCREEN}},
{{TAG|HFSCREEN}},
{{TAG|LRHFCALC}},
[[Hybrid functionals: formalism#Thomas_Fermi|Thomas-Fermi screening]],
[[Hybrid functionals: formalism#Thomas_Fermi|Thomas-Fermi screening]],
[[list_of_hybrid_functionals|List of hybrid functionals]]
[[list_of_hybrid_functionals|List of hybrid functionals]]

Revision as of 19:54, 17 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 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

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

Examples that use this tag