LIBXC1 Pn

LIBXC1_Pn = [real]

Description: LIBXC1_Pn and LIBXC2_Pn, where $n=1, 2, ...$ allow to specify the values of the parameters of the functionals implemented in Libxc that are called with LIBXC1 and LIBXC2, respectively.

For many functionals implemented in the library of exchange-correlation functionals Libxc^[1]^[2]^[3] it is possible to modify the parameters if one does not want to use the default values. If a functional from Libxc has parameters that can be modified, then they are listed in OUTCAR below "Parameters of Libxc functionals:" as P $n$ ( $n=1, 2, ...$ ).

An example is given below for the GGA PBE functional^[4] where the default parameters $\mu=0.21951$ in exchange and $\beta=0.066725$ in correlation are changed to $\mu=10/81\approx0.12345679$ and $\beta=0.046$ to get the PBEsol functional^[5] (of course, the simpler way to use PBEsol from Libxc would be to call it directly with LIBXC1=116 and LIBXC2=133).

GGA = LIBXC
LIBXC1 = 101
LIBXC2 = 130
LIBXC1_P2 = 0.12345679
LIBXC2_P1 = 0.046

For Libxc functionals that are the semilocal component of a hybrid functional, i.e. those with a tag that starts with HYB (and can be used only if LHFCALC=.TRUE.), the following explains how it works for the mixing and screening parameters:

Mixing parameter:
- It is usually one of the parameters LIBXC1_Pn, and can therefore be modified.
- For HYB_GGA_XC_PBEH, HYB_GGA_XC_B1WC, HYB_GGA_XC_HSE03, HYB_GGA_XC_HSE06, HYB_GGA_XC_HSE12, and HYB_GGA_XC_HSE12S, the value of AEXX (even if not specified explicitly in INCAR) will be used and automatically passed to the corresponding parameter in Libxc. On the other hand, if this corresponding parameter (LIBXC1_Pn) is specified in INCAR, then it will be used (instead of AEXX), however note that it will be only for the semilocal component of the hybrid functional and not for the exact exchange that will still use AEXX.
- For all hybrid functionals except those listed just above, AEXX will not be considered for the semilocal component of the hybrid functional, but only for the exact exchange component. Therefore, a particular choice for the mixing parameter has to be done by specifying both AEXX (for the exact exchange) and the appropriate LIBXC1_Pn (for the semilocal component).
- The parameters AGGAX, AGGAC and ALDAC are ignored if the Libxc functional specified with LIBXC1 is an exchange-correlation functional (those with a tag that contains XC, which is the case of the majority of the hybrid functionals).
- The parameter AGGAX is ignored if the Libxc functional specified with LIBXC1 or LIBXC2 is a hybrid exchange functional (i.e., the tag starts with HYB_GGA_X).
Screening parameter:
- It is usually one of the parameters LIBXC1_Pn if it is a screened functional, and can therefore be modified.
- For HYB_GGA_XC_HSE03, HYB_GGA_XC_HSE06, HYB_GGA_XC_HSE12, and HYB_GGA_XC_HSE12S, the value of HFSCREEN (even if not specified explicitly in INCAR) will be used and automatically passed to the corresponding parameter in Libxc. On the other hand, if this corresponding parameter (LIBXC1_Pn) is specified in INCAR, then it will be used (instead of HFSCREEN), however note that it will be only for the semilocal component of the hybrid functional and not for the exact exchange that will still use HFSCREEN.
- For all hybrid functionals except those listed just above, HFSCREEN will not be considered for the semilocal component of the hybrid functional, but only for the exact exchange component. Therefore, a particular choice for the screening parameter has to be done by specifying both HFSCREEN (for the exact exchange) and the appropriate LIBXC1_Pn (for the semilocal component).

Related Tags and Sections

LIBXC1, LTBOUNDLIBXC, GGA, METAGGA, LHFCALC, AEXX, AGGAX, AGGAC, ALDAC, hybrid functionals, settings for specific hybrid functionals

Examples that use this tag

[marques:cpc:2012-1] M. A. L. Marques, M. J. T. Oliveira, and T. Burnus, Comput. Phys. Commun., 183, 2272 (2012).

[lehtola:sx:2018-2] S. Lehtola, C. Steigemann, M. J. T. Oliveira, and M. A. L. Marques, SoftwareX, 7, 1 (2018).

[libxc-3] ttps://libxc.gitlab.io

[perdew:prl:1996-4] J. P. Perdew, K. Burke, and M. Ernzerhof, Phys. Rev. Lett., 77, 3865 (1996).

[perdew:prl:2008-5] J. P. Perdew, A. Ruzsinszky, G. I. Csonka, O. A. Vydrov, G. E. Scuseria, L. A. Constantin, X. Zhou, and K. Burke, Phys. Rev. Lett. 100, 136406 (2008).

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