LMODELHF: Difference between revisions

From VASP Wiki
No edit summary
No edit summary
Line 1: Line 1:
{{TAGDEF|LMODELHF|.TRUE. {{!}} .FALSE.|.FALSE.}}
{{TAGDEF|LMODELHF|.TRUE. {{!}} .FALSE.|.FALSE.}}


Description: {{TAG|LMODELHF}} selects a decomposition of the exchange functional based on a range separated screening,
Description: {{TAG|LMODELHF}} selects a decomposition of the exchange correlation functional based on a range separated screening,
with full exchange in the short range, and {{TAG|AEXX}} in the long range.
with full exchange in the short range, and {{TAG|AEXX}} in the long range.
----
----
If {{TAG|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.
{{TAG|LMODELHF}}=.TRUE. selects the range separated hybrid functional suggested in Ref.<ref name="chen2018nonempirical"/>
The Thomas-Fermi screening length ''k''<sub>TF</sub> is specified by means of the {{TAG|HFSCREEN}} tag.
and Ref. <ref name="cui2018doubly"/> under the name dielectric-dependent hybrid functionals (DDH) and doubly screened hybrid (DSH), respectively. These two functionals are completely identical, but for the way the amount
of exact exchange is determined in the long range limit.
 
The corresponding functional has been implemented in VASP since VASP.5.2 released in 2009 (so way before
the two publications), although the gradient contribution had been erroneously implemented and is only fixed in VASP.6.
The corresponding bug fix has been made available by the authors of Ref.  <ref name="cui2018doubly"/>.


For typical semiconductors, a Thomas-Fermi screening length of about 1.8 &Aring;<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 ==
Line 19: Line 22:
[[specific_hybrid_functionals|settings for specific hybrid functionals]]
[[specific_hybrid_functionals|settings for specific hybrid functionals]]


----


[[Category:INCAR]][[Category:XC Functionals]][[Category:Hybrids]]
[[Category:INCAR]][[Category:XC Functionals]][[Category:Hybrids]]
== References ==
<references>
<ref name="chen2018nonempirical">[https://doi.org/10.1103/PhysRevMaterials.2.073803 W. Chen, G. Miceli, G.M. Rignanese, A. Pasquarello Physical Review Materials 2, 073803 (2018). ]</ref>
<ref name="cui2018doubly">[https://doi.org/10.1021/acs.jpclett.8b00919 Z.H. Cui, Y.C. Wang, M.Y. Zhang, X. Xu, H. Jiang,  J. Phys. Chem. Lett., 9, 2338-2345  (2018). ]</ref>
</references>
----

Revision as of 08:48, 8 May 2020

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

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


LMODELHF=.TRUE. selects the range separated hybrid functional suggested in Ref.[1] and Ref. [2] under the name dielectric-dependent hybrid functionals (DDH) and doubly screened hybrid (DSH), respectively. These two functionals are completely identical, but for the way the amount of exact exchange is determined in the long range limit.

The corresponding functional has been implemented in VASP since VASP.5.2 released in 2009 (so way before the two publications), although the gradient contribution had been erroneously implemented and is only fixed in VASP.6. The corresponding bug fix has been made available by the authors of Ref. [2].


Related Tags and Sections

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

References