LIBXC1 Pn: Difference between revisions

Revision as of 13:32, 7 January 2022

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] 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^[3] where the 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^[4] (of course, the simpler way to use PBEsol from Libxc is to call it directly with LIBXC1=116 and LIBXC2=133).

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

Concerning the mixing and screening parameters of semilocal functionals that are component of hybrid functionals (those with a tag that contains HYB on the Libxc website^[5]), the following should be noted.

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, the choice of the mixing parameter has to be done by specifying both AEXX (for the exact exchange) and the appropriate LIBXC1_Pn (for the semilocal component).
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 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, the choice of the mixing parameter has to be done by specifying both AEXX (for the exact exchange) and the appropriate LIBXC1_Pn (for the semilocal component).

Related Tags and Sections

AGGAX, AGGAC, ALDAC, LHFCALC, 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).

[perdew:prl:1996-3] J. P. Perdew, K. Burke, and M. Ernzerhof, Phys. Rev. Lett., 77, 3865 (1996).

[perdew:prl:2008-4] 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).

[libxc-5] ttps://libxc.gitlab.io

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@@ Line 18: / Line 18: @@
 **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 {{TAG|AEXX}} (even if not specified explicitly in {{FILE|INCAR}}) will be used and automatically passed to the corresponding parameter in Libxc. On the other hand, if this corresponding parameter ({{TAG|LIBXC1_Pn}}) is specified in {{FILE|INCAR}}, then it will be used (instead of {{TAG|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, {{TAG|AEXX}} will not be considered for the semilocal component of the hybrid functional, but only for the exact exchange component. Therefore, the choice of the mixing parameter has to be done by specifying both {{TAG|AEXX}} (for the exact exchange) and the appropriate {{TAG|LIBXC1_Pn}} (for the semilocal component).
-**Screening parameter:
+*Screening parameter:
 **It is usually one of the parameters {{TAG|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 {{TAG|HFSCREEN}} (even if not specified explicitly in {{FILE|INCAR}}) will be used and automatically passed to the corresponding parameter in Libxc. On the other hand, if this corresponding parameter ({{TAG|LIBXC1_Pn}}) is specified in {{FILE|INCAR}}, then it will be used (instead of {{TAG|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 AEXX.