LNOAUGXC: Difference between revisions

Latest revision as of 10:02, 28 February 2025

LNOAUGXC = .TRUE. | .FALSE.
Default: LNOAUGXC = .FALSE.

Description: LNOAUGXC specifies if a METAGGA functional is evaluated with a density that is augmented or not.

The Kohn-Sham kinetic-energy density

[math]\displaystyle{ \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^[1]

[math]\displaystyle{ \tau_{\sigma}^{\textrm{W}}=\frac{\left\vert\nabla n_{\sigma}\right\vert^{2}}{8 n_{\sigma}}. }[/math]

However, this may not always be the case, particularly within the PAW spheres, when the pseudo density is augmented with the compensation charge. If LNOAUGXC=.TRUE. is set in the INCAR file, then the pseudo density is not augmented, which should alleviate the breaking of the condition [math]\displaystyle{ \tau_{\sigma}^{\textrm{W}}\lt \tau_{\sigma} }[/math].

A violation of [math]\displaystyle{ \tau_{\sigma}^{\textrm{W}}\lt \tau_{\sigma} }[/math] can make the calculations unstable, in particular with the TPSS family of functionals.

Mind:

This tag is available since VASP.6.5.0 and is a replacement of the compiler option -DnoAugXCmeta that was available until VASP.6.4.3.
This option may negatively affect the results, therefore it should be used only for functionals, e.g., TPSS, for which the breaking of the condition [math]\displaystyle{ \tau_{\sigma}^{\textrm{W}}\lt \tau_{\sigma} }[/math] may lead to numerical problems.

References

↑ S. Kurth, J. P. Perdew, and P. Blaha, Molecular and solid-state tests of density functional approximations: LSD, GGAs, and meta-GGAs, Int. J. Quantum Chem. 75, 889 (1999).

[kurth:ijqc:1999-1] S. Kurth, J. P. Perdew, and P. Blaha, Molecular and solid-state tests of density functional approximations: LSD, GGAs, and meta-GGAs, Int. J. Quantum Chem. 75, 889 (1999).

[1]

@@ Line 1: / Line 1: @@
 {{TAGDEF|LNOAUGXC|.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|LNOAUGXC}} specifies if a {{TAG|METAGGA}} functional is evaluated with a density that is augmented or not.
 ----
-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, this may not always be the case, particularly within the PAW spheres, when the pseudo density is augmented with the compensation charge. If {{TAG|LNOAUGXC}}=.TRUE. is set in the {{FILE|INCAR}} file, then the pseudo density is not augmented, which should alleviate the breaking of the condition <math>\tau_{\sigma}^{\textrm{W}}<\tau_{\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. and Libxc should be compiled  with the option <code>--disable-fhc</code> has explained [[Makefile.include#Libxc_.28optional.29|here]].
+A violation of <math>\tau_{\sigma}^{\textrm{W}}<\tau_{\sigma}</math> can make the calculations unstable, in particular with the TPSS family of functionals.
+{{NB|mind|
+*This tag is available since VASP.6.5.0 and is a replacement of the compiler option [[Precompiler options#-DnoAugXCmeta|-DnoAugXCmeta]] that was available until VASP.6.4.3.
+*This option may negatively affect the results, therefore it should be used only for functionals, e.g., TPSS, for which the breaking of the condition <math>\tau_{\sigma}^{\textrm{W}}<\tau_{\sigma}</math> may lead to numerical problems.}}
 == Related tags and articles ==
-{{TAG|LIBXC1}},
+{{TAG|METAGGA}},
-{{TAG|LIBXC2}},
+{{TAG|LTBOUNDLIBXC}}
-{{TAG|METAGGA}}
+{{sc|LNOAUGXC|Examples|Examples that use this tag}}
-{{sc|LTBOUNDLIBXC|Examples|Examples that use this tag}}
 == References ==
 <references/>
-----
-[[Category:INCAR tag]][[Category:Exchange-correlation functionals]][[Category:meta-GGA]]
+[[Category:INCAR tag]][[Category:Exchange-correlation functionals]][[Category:Projector-augmented-wave method]]