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 meta-GGA functional from Libxc.
The KS kinetic-energy density should in principle be larger than the von Weizsäcker kinetic-energy density . 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, 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.