LTBOUNDLIBXC: Difference between revisions

From VASP Wiki
No edit summary
No edit summary
 
(38 intermediate revisions by 2 users not shown)
Line 1: Line 1:
{{TAGDEF|TBOUNDLIBXC|.TRUE. {{!}} .FALSE. |.FALSE.}}
{{TAGDEF|LTBOUNDLIBXC|.TRUE. {{!}} .FALSE. |.FALSE.}}


Description: {{TAG|TBOUNDLIBXC}} specifies wether or not the kinetic-energy density <math>\tau_{\sigma}</math> is forced to be larger than the Weizs\"{a}cker <math>\tau_{\sigma}^{\textrm{W}}</math>
Description: {{TAG|LTBOUNDLIBXC}} specifies whether or not the lower bound for the Kohn-Sham kinetic-energy density <math>\tau_{\sigma}</math> (<math>\tau_{\sigma}^{\textrm{W}}<\tau_{\sigma}</math>) is enforced before <math>\tau_{\sigma}</math> is used in a {{TAG|METAGGA}} functional from Libxc.
----
----


For many functionals implemented in the library of exchange-correlation functionals Libxc{{cite|marques:cpc:2012}}{{cite|lehtola:sx:2018}}{{cite|libxc}} it is possible to modify the parameters if one does not want to use the default values. If a functional from Libxc has parameters that can be modified, then they are listed in {{FILE|OUTCAR}} below "Parameters of Libxc functionals:" as P<math>n</math> (<math>n=1, 2, ...</math>).
The Kohn-Sham kinetic-energy density
:<math>\tau_{\sigma}=\frac{1}{2}\sum_{i}\nabla\psi_{i\sigma}^{*}\cdot\nabla\psi_{i\sigma}</math>
should, in principle, be larger than the von Weizsäcker kinetic-energy density{{cite|kurth:ijqc:1999}}  
:<math>\tau_{\sigma}^{\textrm{W}}=\frac{\left\vert\nabla n_{\sigma}\right\vert^{2}}{8 n_{\sigma}}.</math>
 
However, for numerical reasons this may not always be the case and can potentially lead to problems depending on the meta-GGA. If {{TAG|LTBOUNDLIBXC}}=.TRUE. in {{FILE|INCAR}}, then <math>\tau_{\sigma}=\max(\tau_{\sigma},\tau_{\sigma}^{\mathrm{W}})</math> is applied before <math>\tau_{\sigma}</math> is used in a meta-GGA functional from Libxc.
 
However, according to tests, for some of the most common meta-GGA functionals like SCAN{{cite|sun:prl:15}}, a violation of the lower bound is technically not a problem and, furthermore, applying <math>\tau_{\sigma}=\max(\tau_{\sigma},\tau_{\sigma}^{\mathrm{W}})</math> leads to very inaccurate forces and stress tensor. Therefore, by default {{TAG|LTBOUNDLIBXC}}=.FALSE. and Libxc should be compiled  with the option <code>--disable-fhc</code> has explained [[Makefile.include#Libxc_.28optional.29|here]].
 
== Related tags and articles ==
{{TAG|LIBXC1}},
{{TAG|LIBXC2}},
{{TAG|METAGGA}}
 
 
{{sc|LTBOUNDLIBXC|Examples|Examples that use this tag}}
 
== References ==
<references/>
 
----
 
[[Category:INCAR tag]][[Category:Exchange-correlation functionals]][[Category:meta-GGA]]

Latest revision as of 07:10, 12 June 2024

LTBOUNDLIBXC = .TRUE. | .FALSE.
Default: LTBOUNDLIBXC = .FALSE. 

Description: LTBOUNDLIBXC specifies whether or not the lower bound for the Kohn-Sham kinetic-energy density () is enforced before is used in a METAGGA functional from Libxc.


The Kohn-Sham kinetic-energy density

should, in principle, be larger than the von Weizsäcker kinetic-energy density[1]

However, for numerical reasons this may not always be the case and can potentially lead to problems depending on the meta-GGA. If LTBOUNDLIBXC=.TRUE. in INCAR, then is applied before is used in a meta-GGA functional from Libxc.

However, according to tests, for some of the most common meta-GGA functionals like SCAN[2], a violation of the lower bound is technically not a problem and, furthermore, applying leads to very inaccurate forces and stress tensor. Therefore, by default LTBOUNDLIBXC=.FALSE. and Libxc should be compiled with the option --disable-fhc has explained here.

Related tags and articles

LIBXC1, LIBXC2, METAGGA


Examples that use this tag

References