LIBXC1

LIBXC1 = [integer] or [string] 

Description: LIBXC1 and LIBXC2 specify the functionals from the library of exchange-correlation functionals Libxc that one wants to use.

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LIBXC1 and LIBXC2 can be either integers or strings. The available functionals are listed on the Libxc website along with their associated number and tag (e.g., 101 and GGA_X_PBE for PBE exchange). The tag indicates if this is an exchange (X), correlation (C) or exchange-correlation (XC) functional, and to which family it belongs to, namely LDA (LDA or HYB_LDA), GGA (GGA or HYB_GGA) or meta-GGA (MGGA or HYB_MGGA).

The allowed possibilities for LIBXC1 and LIBXC2 are the following:

• Both LIBXC1  and LIBXC2 are specified and correspond to exchange and correlation functionals, respectively, or vice versa.
• Only LIBXC1  (or LIBXC2) is specified and corresponds to an exchange-correlation, exchange or correlation functional. As a side note, the latter choice would, from the physical point of view, make sense only if the correlation is combined with 100% of exact exchange (LIBXC1=1.0). Note also that if LIBXC1  (or LIBXC2) is an exchange-correlation functional, then the other tag can not be used.
• LIBXC1  and LIBXC2 can correspond to functionals of different families, e.g., a meta-GGA and a GGA, respectively.

One has to specify also GGA = LIBXC for LDA, GGA and GGA-based hybrid functionals or METAGGA = LIBXC for meta-GGA functionals (calculations with meta-GGA-based hybrid functionals are not yet possible with VASP).

In addition, many of the functionals implemented in Libxc have parameters that can be modified. This can be done with the tags LIBXC1_Pn and LIBXC2_Pn, where $n=1, 2, ...$ in INCAR.

For calculations with hybrid functionals (i.e., when LHFCALC = .TRUE.), the following explains how it works.

• The Libxc functionals whose tag starts with HYB_LDA_XC, HYB_GGA_XC or HYB_MGGA_XC consist directly of the whole semilocal component of a hybrid functional, and only LIBXC1 (or LIBXC2) can be used (see the example below for PBEh). Furthermore, for these functionals AGGAX, AGGAC and ALDAC can not be used (more informations on how to modify the mixing and screening parameters can be found here LIBXC1_Pn).
• If the semilocal component of the hybrid functional is constructed using Libxc functionals that do not contain HYB in the tag, then (1-AEXX), AGGAX, ALDAC and AGGAC will be used and multiply

$E_{\mathrm{x}}^{\mathrm{LDA}}=\int\epsilon_{\mathrm{x}}^{\mathrm{LDA}}(\rho)d^{3}r$

$\Delta E_{\mathrm{x}}^{\mathrm{GGA}}=\int\Delta\epsilon_{\mathrm{x}}^{\mathrm{GGA}}(\rho,\nabla\rho)d^{3}r = \int\left(\epsilon_{\mathrm{x}}^{\mathrm{GGA}}(\rho,\nabla\rho) - \epsilon_{\mathrm{x}}^{\mathrm{LDA}}(\rho)\right)d^{3}r$

$E_{\mathrm{c}}^{\mathrm{LDA}}=\int\epsilon_{\mathrm{c}}^{\mathrm{LDA}}(\rho)d^{3}r$

$\Delta E_{\mathrm{c}}^{\mathrm{GGA}}=\int\Delta\epsilon_{\mathrm{c}}^{\mathrm{GGA}}(\rho,\nabla\rho)d^{3}r = \int\left(\epsilon_{\mathrm{c}}^{\mathrm{GGA}}(\rho,\nabla\rho) - \epsilon_{\mathrm{c}}^{\mathrm{LDA}}(\rho)\right)d^{3}r$

respectively, where $\epsilon_{\mathrm{x}}^{\mathrm{LDA}}(\rho)=-\frac{3}{4}\left(\frac{3}{\pi}\right)^{1/3}\rho^{4/3}$ and $\epsilon_{\mathrm{c}}^{\mathrm{LDA}}(\rho)=\epsilon_{\mathrm{c}}^{\mathrm{GGA}}(\rho,\nabla\rho=0)$.

Examples of how to specify a Libxc functional in INCAR are given below for the GGA PBE, meta-GGA SCAN and hybrid PBEh (PBE0) functionals.

• PBE

GGA = LIBXC
LIBXC1 = 101
LIBXC2 = 130

or

GGA = LIBXC
LIBXC1 = GGA_X_PBE
LIBXC2 = GGA_C_PBE

• SCAN

METAGGA = LIBXC
LIBXC1 = 263
LIBXC2 = 267

or

METAGGA = LIBXC
LIBXC1 = MGGA_X_SCAN
LIBXC2 = MGGA_C_SCAN

• PBEh (PBE0)

LHFCALC = .TRUE.
AEXX = 0.25
GGA = LIBXC
LIBXC1 = 406

or

LHFCALC = .TRUE.
AEXX = 0.25
GGA = LIBXC
LIBXC1 = HYB_GGA_XC_PBEH

Related Tags and Sections

LIBXC1_Pn, GGA, METAGGA, AEXX, AGGAX, AGGAC, ALDAC, hybrid functionals, settings for specific hybrid functionals

Examples that use this tag

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