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 [[Hybrid functionals: formalism|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. | ||
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