AEXX
AEXX = [real]
| Default: AEXX | = 0.25 | if LHFCALC=.TRUE. |
| = 0 | otherwise |
Description: AEXX specifies the fraction of exact exchange in a Hartree-Fock/DFT hybrid functional type calculation.
The sum of the fraction of the exact exchange and LDA exchange is always 1.0, and it is not possible to set the amount of LDA exchange indepently. Examples: if AEXX=0.25, 1/4 of the exact exchange is used, and 3/4 of the LDA exchange is added. For AEXX=0.5, half of the exact exchange is used, and one half of the LDA exchange is added.
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).
Related Tags and Sections
AGGAX, AGGAC, ALDAC, LHFCALC, hybrid functionals, settings for specific hybrid functionals
Example Calculations using this Tag
bandgap of Si using different DFT+HF methods, Equilibrium volume of Si in the RPA, MgO optimum mixing, Model BSE calculation on Si, Si bandstructure, Si HSE bandstructure