LMODELHF

LMODELHF = .TRUE. | .FALSE.
Default: LMODELHF = .FALSE. 

Description: LMODELHF selects a decomposition of the exchange functional based on a range separated screening, with full exchange in the short range, and AEXX in the long range.

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If LMODELHF=.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_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

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, AEXX, hybrid functionals, Thomas-Fermi screening, settings for specific hybrid functionals

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