LTHOMAS: Difference between revisions
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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 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. | |||
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: | |||
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 Sections == | == Related Tags and Sections == | ||
Revision as of 14:31, 15 February 2011
LTHOMAS = .TRUE. | .FALSE.
Default: LTHOMAS = .FALSE.
Description: LTHOMAS selects a decomposition of the exchange functional based on Thomas-Fermi 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 Sections
LHFCALC, HFSCREEN, hybrid functionals, Thomas-Fermi screening, settings for specific hybrid functionals