LTBOUNDLIBXC: Difference between revisions
No edit summary |
No edit summary |
||
| Line 1: | Line 1: | ||
{{TAGDEF|LTBOUNDLIBXC|.TRUE. {{!}} .FALSE. |.FALSE.}} | {{TAGDEF|LTBOUNDLIBXC|.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 | 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 {{TAG|METAGGA}} functional from Libxc. | ||
---- | ---- | ||
Revision as of 15:42, 10 June 2024
LTBOUNDLIBXC = .TRUE. | .FALSE.
Default: LTBOUNDLIBXC = .FALSE.
Description: LTBOUNDLIBXC specifies whether or not the lower bound for the Kohn-Sham kinetic-energy density [math]\displaystyle{ \tau_{\sigma} }[/math] ([math]\displaystyle{ \tau_{\sigma}^{\textrm{W}}\lt \tau_{\sigma} }[/math]) is enforced before [math]\displaystyle{ \tau_{\sigma} }[/math] is used in a METAGGA functional from Libxc.
The Kohn-Sham kinetic-energy density [math]\displaystyle{ \tau_{\sigma} }[/math] should in principle be larger than the von Weizsäcker kinetic-energy density [math]\displaystyle{ \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 LTBOUNDLIBXC=.TRUE. in INCAR, then [math]\displaystyle{ \tau_{\sigma}=\max(\tau_{\sigma},\tau_{\sigma}^{\mathrm{W}}) }[/math] is applied before [math]\displaystyle{ \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[1], a violation of the lower bound is technically not a problem and, furthermore, applying [math]\displaystyle{ \tau_{\sigma}=\max(\tau_{\sigma},\tau_{\sigma}^{\mathrm{W}}) }[/math] 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.