LTBOUNDLIBXC

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

Description: LTBOUNDLIBXC specifies whether or not the lower bound for the Kohn-Sham kinetic-energy density ${\tau }_{\sigma }$ (${\tau }_{\sigma }^{\text{W}}<{\tau }_{\sigma }$) is enforced before ${\tau }_{\sigma }$ is used in a meta-GGA functional from Libxc.

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The Kohn-Sham kinetic-energy density ${\tau }_{\sigma }$ should in principle be larger than the von Weizsäcker kinetic-energy density ${\tau }_{\sigma }^{\text{W}}={\left|\mathrm{\nabla }{\rho }_{\sigma }\right|}^2/\left(8{\rho }_{\sigma }\right)$. 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., then ${\tau }_{\sigma }=\max ({\tau }_{\sigma },{\tau }_{\sigma }^{\mathrm{W}})$ is applied before ${\tau }_{\sigma }$ is used in a meta-GGA functional from Libxc.

However, according to tests, for some of the most common meta-GGA functionals like SCAN, a violation of the lower bound is technically not a problem and, furthermore, applying ${\tau }_{\sigma }=\max ({\tau }_{\sigma },{\tau }_{\sigma }^{\mathrm{W}})$ leads to very inaccurate forces and stress tensor. Therefore, by default LTBOUNDLIBXC=.FALSE..

Related Tags and Sections

LIBXC1, LIBXC2, METAGGA

Examples that use this tag

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