LTHOMAS

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 k_TF 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.

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