LIBXC1

LIBXC1 = [integer] or [string] 

Description: LIBXC1 specifies the exchange or exchange-correlation functional from the library of exchange-correlation functionals Libxc that one wants to use. If LIBXC1 corresponds to an exchange functional, then it can be used in combination with LIBXC2 for the correlation functional.

N.B.: This feature is available from VASP.6.3.0 onwards that needs to be compiled with -DUSELIBXC.

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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). Note that calculations with laplacian-dependent meta-GGA functionals are not yet possible with VASP.

Libxc is a separate program that has to be downloaded and compiled before VASP is compiled with the corresponding precompiler flag and options.

Important: To get correct results with meta-GGA functionals (see discussion at LTBOUNDLIBXC), it is necessary to use Libxc from version 5.2.0 onwards (or the master version) and to compile it with the option --disable-fhc as explained on the installation page.

The allowed possibilities for LIBXC1 and LIBXC2 are the following:

• Both LIBXC1  and LIBXC2 are specified and correspond to exchange and correlation functionals, respectively.
• Only LIBXC1  is specified and corresponds to an exchange or exchange-correlation functional. Note also that if LIBXC1  is an exchange-correlation functional, then LIBXC2  can not be used.
• LIBXC1  and LIBXC2 can correspond to functionals of different families, e.g., a meta-GGA and a GGA, respectively.

Regarding other tags in INCAR related to Libxc:

• One also has to specify 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). Note that if one of the tags (LIBXC1  or LIBXC2 ) corresponds to a meta-GGA, while the other corresponds to a GGA or LDA, then METAGGA = LIBXC (and not GGA = LIBXC) has to be specified.
• Many of the functionals implemented in Libxc have parameters that can be modified. This can be done via the tags LIBXC1_Pn and LIBXC2_Pn, where $n=1, 2, \ldots$.
• The tag LTBOUNDLIBXC, which is .FALSE. by default, allows to enforce the lower bound on the kinetic-energy density ($\tau_{\sigma}^{\mathrm{W}}<\tau_{\sigma}$) with $\tau_{\sigma}=\max(\tau_{\sigma},\tau_{\sigma}^{\mathrm{W}})$ before $\tau_{\sigma}$ is used in a meta-GGA functional from Libxc.

For calculations with hybrid functionals (i.e., when LHFCALC = .TRUE.), the following provides some explanations:

• The Libxc functionals whose tag starts with HYB_LDA_XC, HYB_GGA_XC or HYB_MGGA_XC (not yet usable with VASP) consist directly of the whole (XC) semilocal component of a hybrid functional. 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).
• The Libxc functionals whose tag starts with HYB_GGA_X or HYB_MGGA_X (not yet usable with VASP) consist of the exchange semilocal component of a hybrid functional. For these functionals AGGAX 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

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

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

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

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

respectively, where $\epsilon_{\mathrm{x}}^{\mathrm{LDA}}(\rho)=-\left(3/4\right)\left(3/\pi\right)^{1/3}\rho^{4/3}$ 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

LIBXC2, LIBXC1_Pn, LIBXC2_Pn, LTBOUNDLIBXC, GGA, METAGGA, LHFCALC, AEXX, AGGAX, AGGAC, ALDAC, hybrid functionals, settings for specific hybrid functionals

Examples that use this tag

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