LIBXC1

LIBXC1/LIBXC2 = [integer] or string 

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

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LIBXC1 and LIBXC2 can be either integers (e.g, 101 for PBE exchange) or strings (e.g., GGA_X_PBE). The list

The amount of LDA correlation included in the hybrid functional can be specified through the ALDAC-tag.

The amount of gradient correction to the exchange and the correlation contributions can be set indepently, however (some popular hybride functionals for instance use only 0.8 of the gradient contribition to the exchange). The GGA flags AGGAX and AGGAC are only used if GGA is already selected (for LDA type calculations no gradient correction will be added regardless of values is used for AGGAX and AGGAC).

Note: The defaults are chosen such that the hybrid PBE0 functional is selected for PBE pseudopotentials (the PBE0 functional contains 25% of the exact exchange, and 75% of the PBE exchange, and 100% of the PBE correlation energy). The resulting expression for the exchange-correlation energy then takes the following simple form:

$E_{\mathrm {xc} }^{\mathrm {PBE0} }={\frac {1}{4}}~E_{\mathrm {x} }~+~{\frac {3}{4}}~E_{\mathrm {x} }^{\mathrm {PBE} }+~E_{\mathrm {c} }^{\mathrm {PBE} }$

Other sensible values are of course AEXX=1.0 (full Hartree-Fock type calculations). In this case, VASP also automatically selects ALDAC=0.0 and AGGAC=0.0, to avoid the addition of a (semi-local) correlation energy.

A comprehensive evaluation of the performance of the PBE0 functional, as compared to PBE, can be found in Ref. .

Related Tags and Sections

AGGAX, AGGAC, ALDAC, LHFCALC, hybrid functionals, settings for specific hybrid functionals

Examples that use this tag

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