LTBOUNDLIBXC: Difference between revisions
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The Kohn-Sham 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>.{{cite|kurth:ijqc:1999}} 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}=(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 <math>\tau_{\sigma}^{\textrm{W}}=\left\vert\nabla\rho_{\sigma}\right\vert^{2}/\left(8\rho_{\sigma}\right)</math>.{{cite|kurth:ijqc:1999}} 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]]. | 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]]. | ||
Revision as of 07:37, 11 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.