LNOAUGXC: Difference between revisions

Revision as of 15:31, 10 June 2024

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

Description: LNOAUGXC specifies if the meta-GGA exchange-correlation functionals are evaluated with a density that is augmented or not.

The KS kinetic-energy density $\tau_{\sigma}$ should in principle be larger than the von Weizsäcker kinetic-energy density $\tau_{\sigma}^{\textrm{W}}=\left\vert\nabla\rho_{\sigma}\right\vert^{2}/\left(8\rho_{\sigma}\right)$ . However, this may not be always the case in particular within the PAW spheres when the pseudo density is augmented with the compensation charge. If LNOAUGXC=.TRUE. in INCAR, then the pseudo density is not augmented with the compensation charge, which should alleviate the breaking of the condition $\tau_{\sigma}^{\textrm{W}}<\tau_{\sigma}$ .

The breaking

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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 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, this may not be always the case in particular within the PAW spheres when the pseudo density is augmented with the compensation charge. If {{TAG|LNOAUGXC}}=.TRUE. in {{FILE|INCAR}}, then the pseudo density is not augmented with the compensation charge, which should alleviate the breaking of the condition <math>\tau_{\sigma}^{\textrm{W}}<\tau_{\sigma}</math>.
+The breaking
-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]].
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Revision as of 15:31, 10 June 2024

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