LTBOUNDLIBXC: Difference between revisions

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{{TAGDEF|LTBOUNDLIBXC|.TRUE. {{!}} .FALSE. |.FALSE.}}
{{TAGDEF|LTBOUNDLIBXC|.TRUE. {{!}} .FALSE. |.FALSE.}}


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 meta-GGA functional from Libxc.
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.
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The KS kinetic-energy density <math>\tau_{\sigma}</math> should in principle be larger than the von Weizsäcker kinetic-energy density <math>\tau_{\sigma}^{\textrm{W}}=\left\vert\nabla\rho_{\sigma}\right\vert^{2}/\left(8\rho_{\sigma}\right)</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.
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, 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..
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.


== Related Tags and Sections ==
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|LIBXC1}},
{{TAG|LIBXC2}},
{{TAG|LIBXC2}},
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[[Category:INCAR]][[Category:XC Functionals]][[Category:metaGGA]]
[[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